Kevlar Thread Guide
Our Kevlar thread is NOT sterile and should not be used when sterile thread is required.
Kevlar Thread Buying Guide
Kevlar (TM) is a Para-Aramid thread. it is one of the strongest and most heat resistant commercially available threads. It is about 2.5 times stronger than nylon and polyester. It also has very little stretch, it does not melt, and it decomposes at 800F. This buying guide helps you select the right thread by explaining Kevlar thread's uses, properties, sizes, specifications, and alternatives that may be better suited.
- Kevlar Thread Uses
- Kevlar Thread Properties
- Kevlar Thread Color
- Kevlar Thread Terminology
- Kevlar Thread Size Overview
Kevlar Thread Uses
Kevlar thread is a great choice for high stress applications including sewing seams on heavy duty clothing, conveyer belts, harnesses, bags, reinforcing plastics, and other fibers. It is also used for high-temperature controls on model airplanes and rockets. We also have a para-aramid yarn that is used for magic tricks.
Kevlar Thread Properties
Kevlar thread is stronger, more heat resistant, less stretchy, and more durable than most other thread types. Thread is usually a very small part of the material content. This means that using Kevlar thread with materials that do not have similar properties is a waste and could be dangerous.
- Decomposition - Kevlar begins to decompose (turn to ash) at about 800F (426C). It can withstand temperatures much higher than nylon or polyester. PTFE Coated Fiberglass has a greater heat resistance than Kevlar, with an operating temperature of 1022F (550C). To put this in to perspective, a disposable butane lighter usually burns at 3578F (1970C). Information - PTFE Coated Fiberglass Thread Guide
- Melting - Kevlar thread does not melt. This is important in fire retardant gear.
- Stretch - Kevlar thread stretches about 2% before it breaks. For example, a 100 foot piece of Kevlar would be 102 feet long just before it breaks. If you sew stretchy fabrics with Kevlar the seams will pucker.
- Acids and Alkalis - Kevlar thread has good resistance to dilute acids and bases. It is degraded by strong mineral acids and to lesser extent, by strong mineral bases. This is important when Kevlar thread is used in a laboratory setting.
- Bleaching and Solvents - Kevlar thread should not be bleached. It has excellent solvent resistance. This matters when Kevlar gear is reused.
- Mildew and Aging - Kevlar thread has excellent resistance to mildew and aging.
- UV Resistance - UV rays will fade Kevlar faster than many other thread types, and prolonged exposure to sunlight and UV rays from even some bright interior lighting causes deterioration. It is recommended to store Kevlar thread in a dark place.
- Abrasion - Kevlar thread has good abrasion resistance.
Kevlar Thread Color
Nobody buys filament Kevlar thread for its color. It normally comes a color called Natural (yellow) and cannot be dyed after it is manufactured. Usually, color is not a problem because it takes a back seat to strength and heat resistance in most applications. There is some black filament Kevlar on the market. We sell it when it is available, but we do not have a steady source for it.
Color may be important when it comes to fire retardant garments, turnout gear, and racing suits. Use Fire Retardant Sewing Thread for sewing seams and attaching patches; use Fire Retardant Embroidery Thread for embroidering names and logos.
Kevlar Thread Terminology
We use several "technical" terms to describe our Kevlar thread. Understanding these terms is important because they affect how you can use the thread:
Bonded and Soft - Bonded means that the thread has a coating that reduces heat at the tip of the needle and prevents unraveling; soft means that the thread does not have this coating. Here are our recommendations:
- Machine Sewing - Use bonded thread for Sizes 69 and higher; in most cases bonding usually does not matter with thinner size thread. Bonding may interfere with adhesives. It can be removed by soaking the thread in alcohol, but it may compromise strength and heat resistance.
- Hand Sewing and Hanging - It does not matter if the thread is soft or bonded.
Monocord - Monocord means that the thread is made with a single ply and has a bonded coating. This gives the thread a flat, ribbon-like shape and makes it usable in double-needle machines. Some of our lighter weight threads use this construction. Machine sewing with monocord often requires a tensioning adjustment.
Left Twist / Right Twist - When threads have more than one ply, they are twisted to the left or the right. Our Kevlar thread is Left Twist unless noted otherwise. This is because single-needle machines made for the U.S. market require left twist or monocord thread. Righ Twist is usually used in double-needle machines.
Loose Twist / No Twist / and Yarn - These kinds of threads are frizzy and almost impossible to put through a needle. Consider them for non-sewing applications such as wrapping and hanging.
Kevlar Thread Size Overview - Thread size is important because there are many considerations. The main ones are:
- Machine Capability - Home, commercial and heavy duty sewing machines have different thread and needle size limitations.
- Needle Size - Needles have sizes that are best suited for specific thread sizes and machine types.
- Stitch Appearance - Are you looking for stitching to be inconspicuous, noticeable, very noticeable, or to be a focal point?
- Strength - Is the thread a suitable strength for what is being sewn? Is it too strong, or not strong enough?
When Kevlar thread's size increases...
- Commercial and Tex Equivalent numbers increase.
- Machine capability requirements increase.
- Thread diameter (surface area) increases.
- Thread strength increases.
- Needle size increases.
- Needle heat and friction increase.
- Stitch visibility increases.
- Fabric ounce per yard increases.
- Yards per pound decreases.
Kevlar Thread - Size 46
Size 46 (Tex 40) Kevlar thread is used on home and commercial machines with a 90/14 to 100/16 needle and has a 14 Lbs tensile strength. It is a lightweight thread used to sew Kevlar fabrics and leather, gear, and fishing tackle.
Kevlar Thread - Size 69
Size 69 (Tex 60 or 70) Kevlar thread is used on home and commercial machines with a 100/16 to 110/18 needle and has a 23 Lbs tensile strength. It is a middleweight thread used to sew Kevlar fabrics, leather, and for reinforcing lighter duty belts. Size 69 (Tex 60 or 70) is the heaviest size most home sewing machines can use. Please note the multiple Tex sizes. Manufacturer availability determines available Tex Sizes.
Kevlar Thread - Size 92
Size 92 (Tex 80 or 90) Kevlar thread usually requires a commercial machine with a 110/18 to 125/20 needle and has a 30 Lbs tensile strength. It is a middleweight thread used to sew Kevlar fabrics, leather, and for reinforcing lighter duty belts. Please note the multiple Tex sizes. Manufacturer availability determines available Tex Sizes.
Kevlar Thread - Size 138
Size 138 (Tex 135) Kevlar thread requires a commercial machine with a 125/20 to 140/22 needle and has a 45 Lbs tensile strength.
It is a middleweight thread used to sew Kevlar fabrics, leather, and for reinforcing lighter duty belts.
Kevlar Thread - Size 207
Size 207 (Tex 210) Kevlar thread requires a commercial to heavy-duty sewing machine with a 140/22 to 180/24 needle and has a 64 Lbs tensile strength.
It is a heavyweight thread used to sew Kevlar fabrics, leather, and for reinforcing lighter duty belts. Stitches are highly visible.
Kevlar Thread - Size 346
Size 346 (Tex 400) Kevlar thread requires a heavy-duty sewing machine with a 236/26 to 280/28 needle and has a 135 Lbs tensile strength.
It is a heavyweight thread used to reinforce belts, and to sew heavyweight and multi-ply fabrics, canvas, leather, and footwear. Stitches are highly visible.
Kevlar Thread - Tex 800
Tex 800 Kevlar thread requires a heavy duty machine with a very large needle and has a 225 Lbs tensile strength. It is used when exceptional thread
strength is required. This heavyweight thread is not bonded and requires a powerful sewing machine. It is used for sewing heavyweight / multi-ply
fabrics, canvas, leather, and footwear, It is also used for non-sewing applications such as binding, reinforcing, hanging, and whipping. Stitches are highly visible.
Kevlar Thread Specifications
Commercial sizing is most widely used thread size standard. Our Kevlar thread shopping selections are listed in commercial sizes. Occasionally we have some off sizes. When this happens, we use the closest Tex Equivalent to the commercial size. Government sizes fall under Military Specification A-A-55220.
Kevlar - Size 46
Commercial Size 46, Tex 40 (T-40), Gov't Size B
Average Strength 14.0 Lbs. (6.3 kg)
Average Thickness 8/1000" (0.008 In) or, 0.21 mm
Recommended Needle Sizes 90/14 to 100/16
Average Yards 312 per Ounce (10,000 per Pound)
Kevlar - Size 69
Commercial Size 69, Tex 60 (T-60) and Tex 70 (T-70), Gov't Size E
Average Strength 23.0. Lbs. (10.4 kg)
Average Thickness 10/1000" (0.010 In) or, 0.25 mm
Recommended Needle Sizes 100/16 to 110 /18
Average Yards 418 per Ounce (6,700 per Pound)
Kevlar - Size 92
Commercial Size 92, Tex 80 (T-80) and Tex 90 (T-90), Gov't Size F
Average Strength 30.0 Lbs. (13.6 kg)
Average Thickness 11/1000" (0.011 In) or, 0.29 mm
Recommended Needle Sizes 110/18 to 125/20
Average Yards 312 per Ounce (5,000 per Pound)
Kevlar - Size 138
Commercial Size 138, Tex 120 (T-120), Gov't Size FF
Average Strength 45.0 Lbs. (20.3 kg)
Average Thickness 14/1000" (0.014 In) or, 0.36 mm
Recommended Needle Sizes 125/20 to 140/22
Average Yards 209 per Ounce (3,350 per Pound)
Kevlar - Size 207
Commercial Size 207, Tex 210 (T-210), Gov't Size 3-Cord
Average Strength 64.0 Lbs. (29.0 kg)
Average Thickness 18/1000" (0.018 In) or, 0.46 mm
Recommended Needle Sizes 140/22 to 180/24
Average Yards 131 per Ounce (2,100 per Pound)
Kevlar - Size 346
Commercial Size 346, Tex 400 (T-400), Gov't Size 3-Cord
Average Strength 135.0 Lbs. (61.2 kg)
Average Thickness 26/1000" (0.026 In) or, 0.65 mm
Recommended Needle Sizes 230/26 to 260/28
Average Yards 66 per Ounce (1,050 per Pound)
Kevlar - Tex 800
Commercial Size N/A, Tex 800 (T-800), Gov't Size N/A
Average Strength 225.0 Lbs. (102.9 kg)
Average Thickness 45/1000" (0.045 In) or, 1.14 mm
Recommended Needle Sizes N/A
Average Yards 32 per Ounce (500 per Pound)
How to Save
Kevlar thread is expensive. It should only be used to sew material that has similar qualities. Here are four ways to save:
- Do you really need Kevlar? - Kevlar seems to have a cult following and customers buy it when less expensive nylon or polyester will do the job. Please, ask yourself or ask us if you really need Kevlar thread.
- Buy what you need - Our junior spools in 1, 2 and 4 Ounces, coils, and thread packs are a great value for specific, one-time jobs and hobbyists. They generally ship 1st Class to U.S. addresses so shipping costs are low compared to price.
- Choose lighter weights - You get more yards per ounce with thinner, lighter weight thread. But, it is important make sure the thread has the strength you need.
- Consider non-standard sizes and closeouts - These threads sell at a 25% to 50% discount compared to our regular thread. We cannot provide certificates of conformance (CERTS) and will likely not restock them in the future. Our closeouts are old thread that sells at very low prices, but is not recommended for machine sewing.
Alternatives to Kevlar - Kevlar costs about 5 times more than nylon and polyester, and it is usually only available in yellow. There are times where other types of thread might be suitable:
Nylon Thread - Use a heavier weight nylon thread instead of a lighter weight Kevlar. For example, a Size 138 nylon thread has about the same strength as a Size 69 Kevlar thread, costs about 80% less, and comes in colors. But, it is twice as thick, not fire retardant, and has 25% elasticity.
Nylon Thread Buying Guide
Polyester Thread - Use a heavier weight polyester thread instead of a lighter weight Kevlar. For example, a Size 138 polyester thread has about the same strength as a Size 69 Kevlar thread, costs about 80% less, and comes in colors. But, it is twice as thick, not fire retardant, and has 25% elasticity.
Polyester Thread Buying Guide
Fire Retardant Sewing Thread - Spun Kevlar and spun Nomex threads have about the same fire retardance as Kevlar thread and are available in many colors. This type of thread is the usually the best choice for sewing seams and attaching emblems and logos. These threads look and feel like cotton because they are made by wrapping fiber around a Kevlar or Nomex core.
Fire Retardant Sewing Thread Buying Guide
Fire Retardant Embroidery Thread - Use Nomex embroidery thread to embroider logos and emblems for fire retardant gear. The thread looks like top-quality, 40 weight, polyester embroidery thread, but it is just as fire retardant as Kevlar thread. It is not strong enough to sew seams or attach emblems. It is very expensive and should only be used when fire retardance is essential.
Fire Retardant Sewing Thread Buying Guide
Filament Nomex Thread - This thread has about the same fire retardance as filament Kevlar, but it only has 1/3 of its strength. It has a smooth, shiny feel. Our closeout filament Nomex is economical, but our newer stock is much more expensive than Kevlar.
Cotton Thread - Cotton is not fire retardant, but it does not melt. It chars, then turns to ash similar to Kevlar. Its strength is comparable to regular sewing thread.
Kevlar Thread Spool Sizes
We sell most of our Kevlar thread in 1, 2, 4 and 16 Ounce (1 Pound) spool sizes or putups. The smaller putups cost more per ounce than the larger ones. But, they are a better choice for one-time jobs, casual sewing, and experimenters. Kevlar thread is sold by weight (ounces, pounds) - not yards. This is because the number of yards-per-pound decreases as thread thickness increases. Selling by weight means prices for a given size spool are about the same across most thread sizes.
All of our Kevlar thread is wound on king spools unless otherwise noted. Most of our 2 and 4 ounce spools are wound in-house, and the spool sizes are consistent for those. Normally, manufacturer spool dimensions are consistent. There are some times one-off occasions where manufacturers will wind 12 and 16 ounce spools with different heights, ranging from 6.5" to 7.5", but the base dimensions remain constant.
Average Spool Dimensions
1 Oz - Base: 2.5", Height: 4.5"
2 Oz - Base: 2.5", Height: 4.5"
4 Oz - Base: 2.5", Height: 4.5"
8 Oz - Base: 3.0", Height: 5.25"
12 Oz - Base: 4.5", Height: 6.5"
16 Oz - Base: 4.5", Height: 6.5"
The inside shaft diameter of all spools described, regardless of base and height, is 1 inch.
For sewing machines not geared to handle these size spools, a Thread Cone Holder may be needed. It is designed to help machines bypass these limitations. There are also DIY thread cone holders that are can be made from PVC pipe, wire coat hangers, or coffee cups most notably. The advantage of a thread cone holder is that it is specifically designed for sewing.
We also carry Hand Stitching Tubes. They are not particularly designed for machine sewing, but customers have created Do-It-Yourself adaptors.
It is important to note that DIY projects can cause machine damage or create tensioning issues if not made properly.
Nominal Spool Weights
Industry norms allow Kevlar thread spool weights to vary by plus/minus 10% from the stated nominal weight. This means that customers get slightly less or slightly more thread than the nominal weight shown on our site. This chart shows our nominal weights and the thread-weight range ( including the spool's weight ) for various sizes. When spools fall within these ranges, we do not charge for when they go over or refund for when they go under. It is important to note that we usually do not charge when a spool goes over the maximum tolerance, but we will always refund when they go below the tolerance.
Nominal 1 Oz Spool - Minimum Spool Weight: 1.3 Oz., Maximum Spool Weight: 2.5 Oz.
Nominal 2 Oz Spool - Minimum Spool Weight: 2.6 Oz., Maximum Spool Weight: 4.5 Oz.
Nominal 4 Oz Spool - Minimum Spool Weight: 4.6 Oz., Maximum Spool Weight: 5.9 Oz.
Nominal 8 Oz Spool - Minimum Spool Weight: 8.0 Oz., Maximum Spool Weight: 10.5 Oz.
Nominal 12 Oz Spool - Minimum Spool Weight: 10.6 Oz., Maximum Spool Weight: 15.5 Oz.
Nominal 16 Oz Spool - Minimum Spool Weight: 15.6 Oz., Maximum Spool Weight: 19.9 Oz.
Certificates of Compliance
We can email manufacturer's CERTS for our 16 Ounce, standard size Kevlar. We cannot provide CERTS for any non-standard size or closeout thread. CERTS apply to specific batch / lots. We wind our smaller spools from the 16 Oz standard size spools and do not keep batch or lot information for these spools. We can send a "representative" CERT for these spools that applies in a general way to the thread purchased. Please call if you must have batch or lot traceable CERTS on small spools and are willing to pay a $2 a spool up-charge.
No Medical Use
Our Kevlar thread is clean in the ordinary sense. But, it is not sterile and using it in any medical device could put lives at risk. We will not knowingly sell Kevlar or any other thread for use in medical devices.
Kevlar thread will propigate flame. It is not fire-proof. Kevlar begins to decompose (turn to ash) at about 800F (426C).