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Why Polyester? - Polyester thread looks, feels, and sews like nylon. You cannot tell the difference just by looking at it just by looking, and technical specifications like strength and stretch are similar. This means that polyester works just as nylon in most applications including: upholstery, leatherwork, auto interiors, banners and flags, sports gear, dog collars, horse saddles and tack, knife sheaths, gun holsters, fishing lures, and brief cases.
So, why use polyester? Polyester does better than nylon when you are sewing things that have prolonged exposure to sunlight, mildew, bleaching, acids, and alkalis. The keyword here is prolonged. Let's say you were sewing a tent; if you plan to leave the tent in the backyard all summer for your children then you should use polyester. If you use the tent for weekend camping trips, then nylon or polyester would work just as well.

Here are examples of things that should be sewn with polyester:

Pool Covers

Tarpaulins

Outdoor Furniture

Banners

Flags

Polyester thread does not provide the ultimate sunlight (UV) resistance. Brands like Sunbrella and Tenara come with replacement guarantees and UV treated nylon and polyester threads will out perform regular polyester. None of this matters if the material sewn is not equally bleach and sunlight resistant. After all, the material makes up at least 90% of the content and cost of the item that is being sewn.

There are times when polyester thread should not be used:

Fire retardant garments and gear - Polyester thread sticks at 440F and melts at 483F. This is too low for any application where thread and material must withstand high temperatures. Use Kevlar, Nomex, and PTFE Fiberglass threads in these situations. Kevlar and Nomex are heat resistant to 700F and do not melt; PTFE fiberglass protects to 1,000F.
Critical need for strength - Polyester thread is strong enough for the kinds of applications described so far. But, it is a bad choice for high stress applications such as conveyer belts because it can stretch up to 25% before it breaks. Size-for-size Kevlar Thread is about twice as strong as polyester and nylon. For example, Size 92 polyester has a 14.5 pound tensile strength; Kevlar in that size has a 30 pound tensile strength. Also, Kevlar only stretches 5% before it breaks.

Technically, our polyester thread is called filament polyester. It should not be confused with these other polyester threads:

Polyester Embroidery Thread - Polyester is rapidly replacing rayon as the first choice for embroidery. It is known for high sheen and standing up to washing and bleach. We have many polyester embroidery threads on our Embroidery and Sewing page and feature Robison-Anton Super Brite Polyester in about 400 colors.
Spun Polyester - Most of the thread used for sewing garments are spun polyesters sold under names like Perma Core and Maxi Lock. They are strong and look an feel like cotton because they are hair thin polyester filaments wrapped in cotton. We have Robison-Anton Spun Polyester 700-yard mini spools for $1.50 and a Spun Polyester Grab Bag of partial spools for $2 a pound.
Factoid - Telling The Difference - Reading the label is always the best way to tell if a thread is nylon or polyester. If there is no label, you can tell by burning the thread in a safe, well ventilated area. Nylon thread (left) burns cleanly and leaves a gray ash. Polyester thread (right) burns brighter, has a foul odor that should not be breathed, and leaves a gooey plastic-like ball.
Polyester Thread Size / Thickness - Polyester thread comes in eleven sizes or thicknesses that range from hair-thin with a 1.5 pound tensile strength to 1 millimeter thick with a 98 pound strength.   Our Polyester Thread Uses / Size Ranges gives recommendations for about 30 typical polyester thread sewing applications. Polyester thread thickness affects almost everything. As thread size increases:

Thread diameter increases - Thread is spongy and thickness cannot be measured with calipers. Instead, thread sizes refer to the weight of a given length of thread. For example 1,000 meters a Size 69 / Tex 70 weighs 70 grams. Also, the tightness of a thread's twist and the bonding (coating) used affect thickness. Having said this, U.S. military specifications for polyester thread include diameters. We include this information on the Polyester Specifications chart.
Thread and seam strength increase - Seam strength is misunderstood when it comes to clothing and lightweight gear. A light-middleweight thread Size 69 / Tex 70 has an 11 pound tensile strength that most people cannot break by pulling. Also, the material sewn costs much more than the thread used to sew it. In most cases (parachutes excepted) it is better for the thread to break have the material fray.
Thread size matters most when it comes to covers and enclosures. In these cases seam stress increases as the area enclosed and tension caused by stretching materials over frames. This means that thread size needs it increase to handle the stress. The tents on the right illustrate this point. The camping tent would use a sizes between 46 and 92; the shelter tent would use thread in the size 207 to 554 range.
Stitch visibility increases - This can be either good or bad depending on how you want your work to look. When you use a thread Size 138 / Tex 135 or higher the stitches become noticeable; at Size 277 / Tex 270 they become a focal point as shown on the right. Also, thread colors that contrast with the material and stitch size increase visibility. Finally, uniform stitching is critical because any mistakes really stand out.

Needle size increases - A thicker thread requires a larger needle. Our Needle and Thread Size Chart and the Polyester Thread Specifications give the range of needle sizes used with each thread size. We give ranges because the physical thickness of thread varies by size. Generally, it is best to use the smallest needle size that has a large enough eye for the thread.
Material thickness increases - Like thread, fabric and leather thickness cannot be measured with calipers. Instead, it is measured by how much a yard of material weighs in ounces. Here is a table that shows how the range of polyester thread sizes used increases as material thickness increases. Note that leather uses thicker thread sizes because it is denser than fabric.
Fabric Ounces Per Yard Thread Size Range Leather Ounces Per Yard Thread Size Range
2 to 6 Ounces 15 to 33 1 to 8 Ounces 46 to 207
6 to 8 Ounces 33 to 47 8 to 12 Ounces 138 to 277
8 to 10 Ounces 46 to 69 12 to 16 Ounces 138 to 346
10 to 12 Ounces 69 to 92 Multiple Layers 207 to 346
12 to 14 Ounces 92 to 207    
Sewing machine requirements increase - Sewing machines work by punching holes in material and forcing thread through the hole to make the stitch. A thicker thread requires a larger hole and a larger hole requires a more powerful machine. Home machines (flat shank needles) usually can handle polyester thread up to Size 69 / Tex 70, commercial machines can handle thread up to Size 207 / Tex 210, and heavy duty (walking foot) machines are needed for sizes 277 / Tex 270 and up.
Yards per pound decreases - Polyester thread is sold by spool weight -- not the length of thread on the spool. For example, a Size 46 / Tex 45 polyester yields about 10,000 yards per pound; Size 207 / Tex 210 yields about 2,100 yards per pound.
Polyester Thread Size Descriptions - Here are brief descriptions of the eleven polyester thread sizes that we stock. See our Polyester Thread Uses / Size Ranges page for size recommendations about specific thread uses, and our  Polyester Thread Specifications page for technical details.
   
Size 15 / Tex 16 / Govt. 00 Ultra thin thread that is mainly used for light sewing and to embroider leather and fabric.
Size 33 / Tex 35 / Govt. AA Lightweight thread that is used for sewing garments and very thin leather such as purses and wallets.
Size 46 / Tex 45 / Govt. B Lightweight thread used for sewing lightweight outdoor gear (e.g. tents), thin leather, and light outdoor garments.
Size 69 / Tex 70 / Govt. E Most popular size, best color selection. Great for lightweight and middleweight sewing. Use for outdoor furniture, leather, gear, garments, upholstery, drapes. Largest size for most home sewing machines.
Size 92 / Tex 90 / Govt. F Middleweight thread that is used for tents, furniture upholstery, auto upholstery, dog beds and collars, sails, and sand bags.
Size 138 / Tex 135 / Govt. FF Middleweight thread that is sometimes used for heavier weight sewing because stitches are noticeable. Typical uses include auto upholstery and convertible tops, awnings, party tents, pool covers, tarpaulins, and sails.
Size 207 / Tex 210 / Govt. 3-Cord Heavyweight thread. Typical uses include auto upholstery, furniture upholstery, boat covers, awnings, tarpaulins, and saddles and horse tack.
Size 277 / Tex 277 / Govt. 4-Cord Heavyweight thread used for hand and machine sewing. Typical uses include horse saddles and tack, knife sheaths, holsters, tarpaulins, banners, boat and pool covers. Its stitches are a focal point.
Size 346 / Tex 350 / Govt. 5-Cord Heavyweight thread used for hand and machine sewing. Typical uses include canvas tarpaulins, saddles, horse tack, shoe repair, conveyer belts, holsters, and sheaths. Its stitches are a focal point.
Size 415 / Tex 410 / Govt. 6-Cord Heavyweight thread used for hand and machine sewing. It is also a survival pack staple. Typical uses include canvas tarpaulins, saddles, horse tack, shoe repair, conveyor belts, holsters, and sheaths. Its stitches are a focal point.
Size 554 / Tex 600 / Govt. 8-Cord Our heaviest thread with a 1 mm diameter. It is used for very heavy duty hand and machine sewing and for tying, binding, and hanging. Stitches are a focal point.
How to Buy Polyester Thread - Here are six things you should know when buying polyester thread:
  • Putups - Putup refers to the amount of thread on a spool. Commercial sewers generally by polyester thread by the pound; hobbyists and casual sewers can save with our two and four ounce spools.
  • Color - Polyester thread comes in many colors. Our color images work well in most cases. But, thread samples may be needed for precise matches.
  • Bonded or Soft? - Most polyester thread has a coating (or bonding) for smoother sewing and less fraying.
  • Monocord -  Regular polyester thread has two or more plies that are twisted together and bonded. Monocord polyester thread is made from hair-thin filaments that are bonded together in a single ply.
  • Elongation - The amount of stretch in the thread
  • Twist - Most polyester has two or more plies that are twisted to the left or right. This affects the types of machines that can use the thread.

Putups - Most of our polyester thread comes in 16, 4, and 2 ounce spools (or putups) as shown on the left. Our commercial customers usually prefer 16 ounce spools for high volume sewing jobs because they cost less per ounce and reduce time lost changing spools. Casual sewers often save by buying the smaller 2 and 4 ounce spools because they avoid paying for thread they will never use. The smaller putups also work well when businesses need to have a variety of colors for repairs.

We stock some of our polyester thread in case quantities at a 10 to 20% discount. Please call if you need a color that we do not stock in case quantities. We will be glad to special order it and give a 10% discount. Lead time is 4 to 6 weeks.

Industry norms allow polyester thread spool weights to vary by plus/minus 10% from the stated nominal weight. This means that you might slightly more or slightly less thread on any spool and use the term "nominal" weight in our descriptions. Here is a table that shows our nominal sizes and the weight ranges for each side including the weight of the spool itself. When a spool falls within these ranges we do not charge for overages or refund underages.
 
Nominal Weight Nominal Minimum Nominal Maximum Nominal Weight Nominal Minimum Nominal Maximum

2 Oz

2.6 Oz

4.5 Oz

8 Oz

8.0 Oz

10.5 Oz

4 Oz

4.6 Oz

5.9 Oz

12 Oz

10.6 Oz

15.5 Oz

6 Oz

6.0 Oz

7.9 Oz

16 Oz

15.6 Oz

19.9 Oz

Polyester thread comes on spools that vary with the putup size:
  • 2 and 4 ounce putups come on spools that are 2.5 inches at the base and 4.0 inches high.
  • 16 ounce putups mostly come on spools that are 4.5 inches at be base and 7.5 inches high.

Some home sewing machines do not have spindles that can handle these polyester spools. We have Thread Cone Holders (right) that solve this problem by feeding thread into your machine.

 
Color - We have polyester thread in over 100 colors. To help with color selection, we divide our color pallet into these colors - black, white, beige, blue, brown, gray, green, orange, purple, red and yellow. Then, we sequence shades from light to dark to make color comparisons easier.

When we add a color, the thread is photographed under controlled lighting conditions. Then, we eliminate highlights and shadows by selecting a small swatch.  Finally, we visually compare the swatch to the spool and make corrections if needed.

This process results in highly accurate color representation on our site. Unfortunately, some things are beyond our control. For example:
  • Colors shown on your monitor change appearance depending on the surrounding lighting and your viewing angle.
  • Your monitor color settings affect the thread looks on your screen.
  • Bonded thread on the spool looks slightly darker than it looks when sewn into fabric or leather.
  • Thread and fabric manufacturers have minor run-to-run color variations.

Please call us at 800-915-2320 when you need a precise color match. We can help by sending a reasonable number of samples, or by having you send the fabric or leather and matching it here.

Bonded or Soft? - A bonded thread has a coating that reduces needle heat and fraying; a soft thread does not have this coating. Bonding only matters if you are using the thread for machine sewing. It makes no difference if you are hand sewing or using the thread to hang or reinforce things.

Bonding does little to help lightweight threads in sizes 46 or lower and soft threads work just as well. It is the norm for threads size 69 and higher. This is why almost all of our threads are bonded.

Monocord - Regular polyester thread is made by twisting two or more plies together and bonding them. Monocord is made from hair-thin polyester filaments that are extruded together in a single ply. Up close, monocord thread is smooth, flat, and ribbon-like. Some say it looks like monofilament fishing line. Here are monocord's advantages and disadvantages:
Advantages:
  • 10 to 14% stronger than twisted thread
  • Runs smoother, fewer needle changes
  • Works with both needles on a dual needle machine.
  • Excels at bi-directional sewing
  • Excels at low profile applications where stitches are buried in the material.
Disadvantages:
  • Machines need to be re-tensioned when switching between twisted and monocord thread.
Bottom line, we do not recommend monocord thread for inexperienced, casual or low volume sewers because of re-tensioning. Monocord has significant advantages for commercial sewing such as upholstery, auto interiors, outdoor gear, and pet accessories.
Elongation - This refers to a thread's stretchiness. Polyester thread has a 26% elongation factor. If you had a 100 foot length of polyester and pulled on it until it snaps, it would be 126 foot long at that point.

Polyester thread's stretchiness is a good thing because It lets seams stretch as fabric or leather stretches. The alternative is seam puckering or the thread snapping. If you are sewing material that does not stretch (e.g. vinyl or cardboard), polyester's 26% elongation factor usually does not matter because material's inelasticity does not stress the thread.

If you are using polyester thread to hang, reinforce or bind, you should consider its elongation. Less stretchy such as  Kevlar, waxed thread, and cord and string are usually better choices.

Twist - Sewing machines designed for the U.S. market use left twist ( also called Z-twist) thread. Almost all of our thread is left twist and the few exceptions are clearly identified as "Right Twist".

Be aware of these situations:

  • Double needle usually require right twist thread in the left needle.
  • Monocord thread does not have a twist and can be used on either side of a double needle machine.
  • Polyester thread's twist does not matter when you are using it for hand sewing, hanging, binding, or hanging.
Polyester Thread Specifications

Here are U.S. military specifications (MIL-DTL-32072 / VT-285F) for polyester thread. Please note:

  • Polyester thread sizes are based on the ratio of a fixed length of thread to its weight - not its diameter. This is because thread is spongy and its diameter cannot be measured with calipers. Bonding increases a thread's thickness.
  • Bonding also reduces the number of yards-per-pound for a given size.
  • Average Break Strength is for twisted thread. Monocord threads are 10% to 14% stronger
  • Metric data is calculated using standard conversion factors. Small rounding differences are inevitable.
  • Needle size ranges come from other sources and are not part of the mil-spec.

Lightweight and Middleweight - Sizes 15 to 138

Size

Tex

16 35 45 70 90 135

Military

A AA B E F FF
Average Break Strength            

Pounds

1.5 3.0 7.0 11.0 14.5 21.0

Metric

0.7 1.4 3.2 5.0 6.6 9.5
Diameter            

Thousandths of Inch

.0047 .0070 .0080 .0107 .0124 .0152

Millimeters

0.1194 0.1778 0.2032 0.2718 0.3150 0.3851
Average Per Pound            

Yards

30,000 12,200 9,500 6,000 4,500 3,000

Meters

27,272 11,090 8,636 5,454 4,091 2,727
Needle Size Range            

U.S.

10-12 12-14 14-16 16-18 18-20 20-22

Metric

70-80 80-90 90-100 100-110 110-120 120-140

Heavyweight - Sizes 207 to 554

Size  

Tex

210 270 350 410 600  

Military

3-Cord / 18 4-Cord 5-Cord 6-Cord 8-Cord  
Average Break Strength            

Pounds

31.0 44.0 53.0 73.0 98.0  

Metric

14.1 22.0 24.1 37.7 44.5  
Diameter            

Thousandths of Inch

0.0186 0.0231 0.0258 0.0283 0.0330  

Millimeters

0.4724 0.5867 0.6553 0.7188 0.8382  
Average Per Pound            

Yards

2,100 1,500 1,300 1,000 630  

Meters

955 682 591 455 286  
Needle Size Range            

U.S.

22-24 24-26 26-28 28-30 30-32  

Metric

140-180 180-220 220-260 260-300 300-360  
 
Polyester Thread Usage and Size Guide

Here are 19 sewing applications that typically use polyester thread and the range of thread sizes that can be used with each. There is no right size for any application because four things have to be balanced: material thickness and density; seam strength requirements; stitch visibility preferences; and sewing machine capabilities. Often, the "right" thread size is a compromise that balances these competing needs.

Automobiles - Both nylon and polyester thread work well for automobile seats and interiors. Use polyester for convertible tops and covers.
  • Upholstery - Use sizes ranging from 69 to 415 depending on stitch visibility.
  • Convertible tops - Use sizes 92 to 207 depending on fabric thickness. Use heavier thread sizes when stitch visibility is required.
  • Automobile covers - Use sizes 46 to 207 depending on fabric thickness and density.
Awnings - Polyester thread is the first choice for awnings used outdoors. Indoor awnings can be sewn with nylon or polyester.
  • Lightweight (bed canapés) - Use sizes 46 or 69.
  • Middleweight (patio umbrellas) - Use sizes 92 to 207
  • Heavyweight (see left) - Use sizes 138 to 554 depending on awning size.
Backpacks - Nylon and polyester thread work equally well when backpacks spend most of their time in storage. Polyester is better when backpacks are kept outdoors most of the time.
  • Children's backpacks and book bags - Use sizes 46 to 69.
  • Hiking and camping - Use sizes 69 to 138.
  • Military style - Use sizes 92 to 207.
Banners and flags - Nylon and polyester work equally well when banners and flags are used indoors or taken outside on special occasions. Use polyester thread for banners and flags are used outdoors for an extended time.
  • Lightweight vinyl - Use sizes 33 to 92 depending on vinyl density.
  • Mid-size (see picture) - Use sizes 92 to 207.
  • Large banners - Use sizes 138 to 554.

Note: When banners are stretched to prevent sagging, it puts stress on seams. Thread thickness requirements increase as banner area increases.

Boating - Polyester thread works well for boat upholstery, sails, canapés, and covers because of its UV, moisture, and mildew resistance. There are threads designed for marine use that we do not sell. They outperform polyester over time. But, they are pricey.
  • Upholstery - Sizes range from 46 to 207 depending on stitch visibility preferences
  • Sails - Use sizes 46 to 92 for lightweight vinyl and nylon. Canvas sails use sizes 92 to 346 depending on seam stress.
  • Canapés and covers - Thread sizes range from 69 to 207 depending on size and seam stress.
Boots - Both nylon and polyester thread are used for boots and shoes and work equally well:
  • Decorative stitching - Use sizes 15 to 46 depending on pattern density. Consider Robison-Anton Polyester Embroidery Thread for intricate patterns.
  • Upper seams - Use sizes 69 to 207 depending on stitch visibility.
  • Attaching soles - Use sizes 207 to 346. Sizes 415 and 554 are sometimes used to make welts a focal point.
Bookbinding - Polyester thread is the first choice when stitching is visible and books are expected to have a long shelf life. This is because polyester's UV (sunlight) resistance retards yellowing. Nylon and spun polyester work just as well with hidden stitches or books that do not need to last.

Bookbinders typically use sizes 69 to 138. Heavier threads are used when having stitches become a focal point is needed. Bookbinding requires heavy duty machines that can go through leather and paper.

Clothing - Most garments are sewn with lightweight spun polyester and cotton. But, there are exceptions where nylon and polyester threads predominate:
  • Outdoor coats and jackets use sizes 33 to 69.
  • Leather coats and jackets use sizes 69 to 138. Heavier thread sizes are sometimes used to make stitches stand out.
  • Dressy leather gloves use sizes 15 to 46; gardening gloves use sizes 33 to 69; and work gloves use sizes 46 to 92.

 Note: First responder clothing and gear should use Kevlar or Fire Retardant Thread.

Covers - Nylon and polyester work equally well when covers are mainly used indoors. Use polyester for covers used outdoors.
  • Lightweight (vinyl and nylon) - Use sizes 46 to 69.
  • Middleweight (tents, boat covers) - Use sizes 92 to 207.
  • Heavyweight (truck covers, tarpaulins) - Use sizes 138 to 346 depending on material thickness and cover size.
Curtains - The choice between nylon and polyester comes down to how much direct sunlight the sewn area will receive. Also, spun polyester, cotton and monofilament are used for shear see-through curtains:
  • Lightweight (shear) - Sizes 15 to 46.
  • Middleweight (drapes) - Sizes 69 to 138 depending on the material thickness.
  • Heavyweight (stage) - Sizes 138 to 346.
Furniture upholstery - Nylon thread predominates with indoor furniture, but polyester works just as well.
  • Cloth cushions - Use sizes 69 to 138.
  • Cloth upholstery - Use sizes 92 to 207.
  • Leather upholstery - Use sizes 92 to 277.
Leatherwork - Nylon and polyester thread work equally well with leather. Thread size mostly depends on how stitching is supposed to look:
  • Belts - Use sizes 69 to 277.
  • Horse tack, harnesses, saddles - Use sizes 207 to 415.
  • Holsters - Use sizes 207 to 346.
  • Knife sheaths - Use sizes 138 to 277.
  • Wallets - Use sizes 46 to 207.
Luggage and carrying cases - Nylon and polyester work equally well. Thread size depends on case size. Leather cases sometimes use heavier threat sizes for stitch visibility.
  • Computer cases - Use sizes 69 to 92.
  • Duffel bags - Use sizes 46 to 138
  • Gun cases - Use sizes 69 to 207
  • Luggage - Use sizes 69 to 207.
  • Musical instrument cases - Use sizes 69 to 138
Motorcycles - Use nylon or polyester thread for motorcycle seats or saddlebags. Polyester is better if the motorcycle is left outdoors most of the time. Thread sizes depend on how stitching is supposed to look,
  • Covers - Use sizes 92 to 207.
  • Leather clothing - Use sizes 69 to 138.
  • Saddlebags - Use sizes 138 to 277.
  • Seats - Use sizes 138 to 346.
Patio furniture and accessories - Use polyester thread whenever possible.
  • Cushions - Use sizes 46 to 138.
  • Chairs and chaises - Use sizes 69 to 207.
  • Pool covers - Use sizes 92 to 346 depending on the area covered.
  • Umbrellas - Use sizes 138 to 277 depending on fabric thickness.
  • Webbing - Use sizes 69 to 138 to fasten webbing to frames.
Pet accessories - Nylon and polyester thread work equally well with leather and fabric. Size depends mostly how stitching is supposed to look. Seam strength is a secondary consideration. Cat accessories use thinner thread than dog accessories; and fabric accessories use thinner thread than leather accessories.
  • Collars - Use sizes 69 to 207.
  • Leashes - Use sizes 46 to 207.
  • Pet carriers - Sizes 69 to 138.
  • Pet clothing - Use middleweight spun polyester or cotton.
  • Pet toys - Sizes 46 to 92.  Determined pets can chew through any thread - even Kevlar
Restaurant decor - Use nylon or polyester thread for indoor furnishings. Use polyester for outdoor patio furniture.
  • Bar stools - Use sizes 46 to 92.
  • Booths - Use sizes 69 to 207.
  • Chairs - Use sizes 33 to 92.
  • Cushions - Use sizes 46 to 138.
Snowmobiles - When snowmobiles are garaged indoors nylon and polyester thread work equally well. Use polyester thread if they are kept outside and for all covers.
  • Covers - Use sizes 92 to 207.
  • Seats - Use 138 to 346 depending on stitch visibility.
  • Snowsuits - Use sizes 46 to 92.
Tents - Use either nylon or polyester thread for small recreational tents used on camping trips. Use polyester thread for tents that stay outdoors most of the time. Seam stress increases as the area covered by the tent increases. This means that thread size needs to increase accordingly:
  • Small camping tents - Use sizes 46 to 92.
  • Mid-size party tents - Use sizes 92 to 207.
  • Large event tents - Use sizes sizes 207 to 554.

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