Selecting the proper thread for denim garments is very important to minimize sewing and seam performance issues. There is an old saying that:

Thread only makes up a small percent of the cost of the finished product … but shares 50% of the seam responsibility.

Unquality Examples


Restitched Seams
 

Broken Stitch on Waistband

When you talk about sewing denim, five key issues that need to be addressed are:

1. What weight denim is being sewn?
2. What seam appearance, boldness of stitch, do you need?
3. What wash process will the jeans see?
4. What is the after wash color that you desire?
5. What degradation issues need to be addressed?

Core Spun Threads
Cotton Wrapped Polyester Core -
D-Core®

Poly Wrapped Polyester Core -
 Perma Core®

Some designers prefer the thread to wash-down during the wash processes and, if this is the case, you would select D-Core® Cotton-Wrapped Core thread. Degrees of color fastness will vary with particular shades. With this known factor, a user of D-Core® Cotton-Wrapped Core should look at all wash codes to insure the thread color will be appropriately maintained. We also recommend doing pre-production wash testing to assure that the wash-down look will be acceptable.

On the other hand, many jean designers want the thread to maintain its color for the life of the garment and offer a signature look. If color fastness is key, then select Perma Core® Polyester-Wrapped Core thread. Also with Perma Core® Polyester Wrapped products, you have the option of picking the desired color from a color palette to obtain the look you want after the wash procedures. This will allow a more controlled shade, which will be maintained after continual washes by the consumer. We still recommend doing pre-production wash testing prior to going into production.

D-Core® Cotton-Wrapped and Perma Core® Polyester Wrapped Core threads offer excellent abrasion resistance to the varied wash codes that a pair of jeans may be exposed to. While most of the wash codes in the USA are now a combination of chemicals and stone to obtain the desired look, stone is still predominately used outside the USA.

Other Thread Types Used in Denim

Spun Polyester
Spun polyester threads like A&E’s Perma Spun® or Excell® are made from staple fibers that are spun into a singles yarn and then plied to make the sewing thread.  They are also commonly used in denim particularly as a looper thread or serging thread to minimize the thread cost.  However, spun polyester threads are much weaker than the same size of corespun thread and are not as durable to chemicals and abrasion.  In many cases a larger spun polyester thread will be required even on the inside loopers and overedge seams to maintain seam strength.  For example, many manufacturers are using a T-40 corespun thread for serging but they may need to use a T-45 (40/3) or T-60 (30/3) to obtain similar seam performance.  Using larger thread sizes increases the cost of thread in the garment.

Air Entangled
Air entangled polyester threads like A&E’s Magic® are made from continuous filaments of polyester thread that have been entangled together into a cohesive bundle and then heat set to make the finished thread.  Because air entangled threads are not made in a plied construction, they are very flat and ribbon like.  This allows them to have superior abrasion resistance and makes them less susceptible to cut or broken stitches.  Air entangled threads are much stronger the comparable size spun polyester threads and are ideal for loopers and overedge seams to help reduce the thread cost while producing a more durable seam.

Thread Size

Both of these thread types are available in sizes to meet the variety of denim fabric weights. From a Tex 40 to a Tex 150, you can achieve the desired performance throughout the sewing floor and after the varied finishing processes. Use the correct size to obtain the desired look while maintaining seam integrity. Some basic sizes used in today's denim are listed in the table below:

Many times this problem occurs when a previously sewn stitch line is crossed during a subsequent operation and the needle damages the thread in the seam. Broken stitches can also occur when there is excessive abrasion or chemical degradation of the thread during the wash process. Let's now discuss what are some of the major causes and solutions to these problems.

Unquality Examples


Broken Stitch on Wasteband

Broken Stitch on Seat Seam

Solutions

1) Many manufacturers have significantly reduced the number of "cut" and "broken" stitches by using high-performance sewing threads. Make sure the correct thread type and size are being used in both the needle and bottom (looper) positions. Core threads that have a continuous filament polyester core in each singles yarn are more resistant to cutting and degradation than 100% spun polyester threads and other thread constructions.

2) Usually the larger the thread size, the more resistant the thread is to being cut by the needle or feed or to failure due to chemical degradation or heat. Because of this many manufacturers have increased the thread size on critical operations like waistbanding, seat seaming, etc. Typical thread sizes used on heavy denim run from T-150 down to T-60 depending on the desired look. Typical thread sizes used on twills used in the manufacturing of chinos run from T-40 to T-60.

3) Inspect the needle point at regular intervals and check for sharp or burred points. If the needle point is damaged, replace the needle. Many companies have found that it is best just to replace the needle on critical operations once or twice a day.

4) Use proper thread tensions.  Make sure the stitch on the seam line is loose and be able to move if the needle hits it during a subsequent sewing operation.  This will also allow the stitch to flex during washing minimizing broken stitches.  Tight machine thread tensions will not allow proper flexibility in the stitch and will increase "cut-stitch" damage.  Generally, on chainstitch seams, the ideal stitch balance is when the needle loop on the underside of the seam lays over half way to the next needle penetration.  This can be checked by unraveling the looper thread and observing the needle thread on the underside of the seam.

5) Check the edges of the needle plate and presser foot needle holes to make sure they do not have any sharp edges or burrs that can damage the thread during sewing.  Properly remove all burred or sharp surfaces making sure not to oversize the needle holes which can lead to excessive "flagging".

6) Inspect the feed dogteeth directly behind the needle holes and make sure they are not sharp. If required, buff the feed dog teeth with a wire wheel or with a stone if they appear to be sharp. Be careful not to remove too much of the feed dog teeth that could hinder the feeding or interfere with chaining.

7) Use the minimum amount of presser foot pressure to get a uniform stitch length. Excessive presser foot pressure can cause the thread to be damaged when it is compressed against a relatively sharp surface. On some machines it is sometimes necessary to use a presser spring with fewer coils per inch to give more consistent pressure even when crossing heavy seams.

8) The proper type and capacity folder should be used to prevent stalling when crossing heavy seams. Feed stalling will increase the chances of "cut" stitches.

9) Check for signs of needle heat or excessive heat exposure during laundering that may be melting the thread.  Usually, if the thread has been damaged by heat, the thread will have a hard melted surface that can be felt or seen using a magnifying glass.  If you suspect that needle heat is a problem, try using a special coated needle or needle coolers to reduce needle heat.  Make sure the thread has the proper type and amount of lube.  Most major thread suppliers have developed high-performance lubricants to minimize heat damage on polyester threads.  A cotton wrapped core thread may be more resistant than a 100% polyester thread.

Damage Done During Pre-Washing

Sometimes partially damaged thread from the sewing operation will fail during stone washing or other processes. Most of the time this damage is difficult to detect but should be investigated using the suggestions mentioned on the previous pages. On the other hand, many seams are damaged during the wash processes due to excessive abrasion, chemical degradation, and heat degradation. To reduce damage to the thread in the seams, we suggest the following:

• Make sure the correct fiber type, thread construction, and size are being used. For example, 100% polyester like A&E's Perma Core® much more resistant to enzymes and chemicals as compared to cotton threads.

• Work with your laundry to develop standards with regard to the type and amount of chemicals, rocks, cycle times, and temperatures that are being used in both the washing and drying processes. You should monitor and properly test the following:

1. Any changes of rocks and chemicals from one vendor to another
2. Changes of cycle times
3. Changes in temperature during the washing or drying cycles

Evaluate the best way the garment should be processed, whether it should be inside-out or right-side-out, the fly buttoned or not buttoned, etc. Care should be taken if the garments are turned right-side-out when they are still wet. Extra moisture in the garments can cause excessive whipping of the bottom hem seam causing excessive damage.

Thread Cost

Corespun threads generally have a higher purchase prices than spun polyester and air entangled threads. However, the total cost of thread, which should include any additional maintenance costs related to thread sewing and seam performance, generally makes corespun thread a real value.

Ways of Reducing Cost

In today's competitive market place, everyone must be concerned about costs. Ways of reducing thread cost without sacrificing in performance might include:

• Using high performance threads like Perma Core® and D-Core® that reduces down time and rejects due to seam failure and minimizes repairs after laundry.  Repair rates in the in the laundry can be as high as 20% to 30% when using spun polyester sewing threads.  Our experience is that, if Perma Core® and D-Core® are used along with the other recommendations mentioned above, these repair rates would drop to less than 2%.  This can result in a sizable cost savings in the laundry that usually overcomes the higher initial purchase price of core thread versus spun.  (See the PDF file for Performance Gains Using A&E Core Thread .) 
• Using smaller thread sizes (example: using T-40 corespun thread on serging or using T-60 corespun thread in loopers on main seams instead of a heavier topstitch thread size..
• Using natural or white instead of dyed thread on the loopers or inside threads.  Natural D-Core® threads are less expensive than vat dyed, D-Core® threads.  White Perma Core® threads are less expensive than vat dyed, Perma Core® threads.  This can reduce your thread cost by as much as 10 to 12%.
• Using a less expensive thread construction on non-critical seams. This might include using Perma Spun® (spun polyester) or Magic® (entangled threads) as looper threads or serging threads on the inside of the garment.

A&E has an excellent Technical Service Team to assist with any questions you may have concerning thread application or thread specifications for any denim fabric you will sew. Also, they will be able to mak e recommendations on the correct needle size and machine setup for obtaining the maximum efficiency for each operation.