The Ultimate Buyer's Guide for Purchasing para aramid yarn

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.

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Information Topics

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 F (550C). To put this in to perspective, a disposable butane lighter usually burns at F (C). 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. Right 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 Descriptions

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-.

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/" (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/" (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/" (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/" (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/" (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/" (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/" (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.

Information
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.

Information
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.

Information
Fire Retardant Sewing Thread Buying Guide

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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.

Information
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.

Spool Dimensions
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"
Inside Diameter
The inside shaft diameter of all spools described, regardless of base and height, is 1 inch.
Comments
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 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.

Safety
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.

Fire Resistance
Kevlar thread will propigate flame. It is not fire-proof. Kevlar begins to decompose (turn to ash) at about 800F (426C).

Personal protective equipment (PPE) is highly regulated and required by many trades. With so many types of PPE on the market like Kevlar, which is a common brand of para-aramid materials, and high-performance polyethylene (HPPE) composite yarn, it is difficult to know which material will perform best in your environment for your workers. To make the decision easier, here&#;s a breakdown of the pros and cons of para-aramids and HPPE.

Strength & Durability

Kevlar

Kevlar (para-aramid materials) was introduced on a commercial scale as PPE in the s and 70s. To this day, it is known for its strength. At the point of creation, para-aramid fibers have a strength of around 2.03/2.06 N/tex. N/tex is the same as GPa/g/cm^3  &#; these equate to one million newton-meters per kilogram. N/tex is a measure of force per linear density. 

Para-aramid fibers are synthetic fibers joined through hydrogen bonds in rigid polymer chains. The process to make para-aramid fibers, as well as their crystalline structure, leaves them vulnerable to weakening over time.

What Weakens Para-Aramid Fibers?

Para-aramid fibers are naturally yellow. Any additive, including dyes, weakens these fibers. That being said, washing para-aramid fibers also compromises their hydrogen bonding and leaves the material weaker than when it came out of the factory. 

In general, para-aramid fibers lose 15 percent of their strength after eight wash cycles. This percentage could be even larger if bleach is added to the laundry, as that makes the fibers decompose. With many detergents having a small amount of bleach included in the solution, this increased distress to the material is not always completely avoidable. 

Ultraviolet rays and moisture also weaken the material. This means para-aramids are not ideal for outdoor work environments where the sun is shining and people are sweating. Any moisture, such as a person&#;s sweat, will elongate the fibers. When the fibers stretch out the molecular makeup of the material is altered. Para-aramid fibers are also heavier than HPPE fibers on average, making it a hotter and less breathable material to work in and increasing the likelihood of a person to perspire.

HPPE

HPPE has the highest tensile strength to mass ratio of any fiber available. It is 15 times stronger than steel, with a tensile strength of about 3.8-3.9 N/tex. Its molecular makeup is slick and chemically inert, making the material more resistant to abrasion compared to para-aramid fibers. It is also stronger when encountering a strong abrasive force. 

HPPE is unaffected by moisture (e.g. sweat) or UV radiation. This means it is able to maintain its molecular integrity despite harsh working environments, such as summer days in the Southeast United States inside non-environmentally controlled plants or in direct sunlight. 

Because of its ability to withstand abrasion and its overall strength, HPPE materials are the best products for people in the glass, waste recycling, knife sharpening, food processing, sheet metal production, and automotive manufacturing industries.

Temperature

Kevlar

Para-aramid fibers do not melt. However, they will begin to degrade at temperatures above 500°C. This means they do not burn until exposed to temperatures of almost 1,000°F. For this reason, para-aramid fibers are often used by military troops. The strength of para-aramids and their ability to withstand extreme temperatures make them great protective equipment in combat zones where hostile attacks can come quickly and without warning. 

Para-aramid fibers are also best suited for people who work on or in close proximity to furnaces/fires or with welding equipment. These fibers are frequently the main PPE material used by firefighters.

HPPE

HPPE is a polyethylene plastic, which means it burns quickly. HPPE begins to dissolve at temperatures of 220°F or greater, which poses a safety risk to people who are working in high temperatures environments. 

Rather than burning, polyethylene melts at high temperatures. This is an advantage when you want to recycle the material, but a disadvantage if that hot, liquified plastic comes into contact with a person&#;s skin. HPPE, therefore, should not be used where unexpected high temperatures could occur, since the material could melt onto a person&#;s skin, leaving significant burns. For this reason, HPPE fibers are outlawed from use for military clothing contracts.

Customization

Kevlar

As previously stated, Kevlar is a shade of yellow in its naturally produced form. Remember, when the color or breathability of the material is altered, the material becomes weaker. For instance, the military often requests black para-aramid fibers for camouflage. While the difference in strength is not directly visible to the person wearing the clothing, it is apparent and can also reduce the longevity of the product. Para-aramid fibers are best kept as is when they exit the spinnerets from dry jet wet spinning.

HPPE

HPPE is totally customizable. Its fibers are produced through a gel spinning process and their molecular makeup does not weaken as a result of additives. Therefore, customers can have softeners, dyes, oils, and different protective fibers added to their HPPE without consequence. HPPE can also have ANSI hi-vis polyester and reflection visibility tape added to the product to make it more visible for construction work or work in hazardous areas, such as along highways. 

Manufacturers have started to blend CBD oil with HPPE to help with pain maintenance and promote a calm work environment. Manufacturers also frequently add cotton or other soft materials to make the PPE more appealing and comfortable for workers. Another common customization is adding thumb holes, thumb loops, and mesh backs. 

The thumb holes and loops prevent the PPE from shifting while workers move their elbows or lift heavy items, and the mesh back increases breathability and promotes cooling. With all of HPPE&#;s customizable features, molecular strength, and flexibility, it typically requires a greater front-end investment compared to para-aramids. However, the durability of HPPE products can lead to cost savings in the long term, as they are replaced much less frequently than para-aramid PPE.

The Verdict

Here are the &#;winners,&#; based on the elements we outlined in this article. The preferred PPE material when considering the following elements are:

High Temperature &#; Kevlar Para-aramid PPE wins

• Para-aramid fiber is the preferred PPE in environments that are exposed to high heat.
• This is the preferred material when it comes to working in firefighting, welding, working near furnaces, etc.

Strength & Durability &#; HPPE wins

• HPPE is a much stronger material (tenacity) than Kevlar (para-aramid fabric) and is highly cut and abrasion-resistant.
• HPPE does not degrade from UV light and sweat like Kevlar para-aramid PPE and can last up to 6x longer. 
• This is the preferred material when it comes to working in glass, waste recycling, knife sharpening, food processing, sheet metal production, and automotive manufacturing industries, among others.

Customization &#; HPPE Wins

• HPPE composite yarns are totally customizable without compromising their superior strength.
• Kevlar para-aramid PPE weakens as a result of additives and custom colors; thus, it needs to be replaced more often.

Ultimately, there is no right or wrong material. Your choice will depend on your working environment. However, now that you know the strengths and weaknesses of each material and the environments they&#;re best suited for, you can make an informed decision that you feel good about.

Are you interested in learning more about para aramid yarn? Contact us today to secure an expert consultation!