I learned a new thing about polyester thread!


Sew Fine! thread from Superior.

What do you do when you find out that something you thought was true, really isn’t? If you are me, you write a blog post for all the world to see :-).

NOTE: I did, in fact, find out a little more and the updated information is in this post (https://wordpress.com/post/pieceocakeblog.com/12789).

If you have ever been in my class, you know that I use cotton thread with cotton fabric. That’s not going to change because cotton thread has many characteristics that I like. However, one of the main reasons I have not recommended using polyester thread is that I believed that it might degrade faster than cotton over time. This was based on old information that may have true back in the day but is no longer relevant.

I have been doing quite a bit of research on thread and I ran across this academic study  that looked at the biodegradability of polyester vs. cotton. You can read the whole paper, or skim it, but here’s the very short story:

The researchers took cotton and polyester jersey fabrics and subjected them to the same treatment. All fabrics were laundered 30 times with various washing products to simulate garments at the end of their useful lives prior to testing. They were then buried and composted for 3 months.

“The polyester fabric showed a slight initial degradation, but the fabric was still intact after testing under both laboratory conditions and the compost environment. In soil and compost testing, which included multiple organisms and enzymes, the cotton fabric with softener had an accelerated degradation rate, while the cotton fabric with resin showed a relatively slow degradation rate.

All cotton samples were more significantly degraded in the compost environment than under the laboratory conditions and confirmed to be ‘compostable’.”

I’ve been wrong about this aspect of polyester thread. I still don’t love it for the kind of sewing that I do. Polyester thread doesn’t tolerate high heat from an iron, it is slippery, and it is shinier than cotton. But there is nothing suspect about the fiber itself. If you have a place where it makes sense to use polyester, go for it. Who knows… it’s possible I might find myself using it in some future project.

Lastly, it is true that polyester is basically a plastic. Many of us, me included, are trying to cut back on the amount of plastic we use. However, until we manage to cut out much bigger sources of plastic in our lives, I think it’s safe not to obsess about the plastic in polyester thread.

20 thoughts on “I learned a new thing about polyester thread!

  1. Thank you for the information. I’ve been hearing that quilters are using more polyester threads. Would you ever use it for piecing with cotton fabrics?


    • Probably not, and here’s why:

      Cotton has a natural texture that grabs the fabric well. It doesn’t tend to come unstitched at the end of a seam. Polyester thread can be slippery which leads to stitches unraveling a bit. That said, I freely admit that I have not sewn with every poly thread on the market.

      Cotton tolerates higher heat than polyester. I don’t know about you, but my iron is set to super hot most of the time and that might not be great for polyester thread.

      Poly/cotton blends stay in the seam much as cotton thread does, and they tolerate higher heat. But poly/cotton is going to produce lint in the same way that cotton does (in varying amounts depending on the quality of the thread). For myself, since I like cotton thread a lot, I would choose 100% cotton over a blend.



    • I have always used cotton thread in the machine for piecing. I think the main reason some people don’t is that cotton produces more lint than polyester.

      I don’t mind cleaning my machine, it’s just part of the sewing process. I clean and oil the bobbin area every time I change the bobbin.

      If you aren’t cleaning and oiling the bobbin area often, you should read your owner’s manual and at least find out how often you should be oiling it.



  2. have you Superior Thread? I use Bottomline exclusively in my bobbin and works great for hand sewing (no tangles or breaking). This is a 60 weight polyester thread. You will love it.


    • No, I haven’t used Bottom Line but I do plan to compare it to the thread I normally use. I have compared most of the cotton threads on the market to the threads I use often. I’ve never looked closely at many of the polyester sewing threads but I will and I’ll do it with an open mind.

      It’s so easy to fall into the idea that the thread you are using (and liking) is always the best choice. I’m as guilty of that as everyone else. The key is to remain open-minded and stay informed. You never know when you might find a better thread.



  3. I was once told that if I used polyester thread to piece cotton fabrics that, over time, the seams would begin to fail due to the polyester being stronger than the cotton fibers. The theory was that the poly would “cut through” the cotton fibers. I have no evidence of this happening. Have you ever heard this?


    • That may have been true a long time ago, when polyester thread was much stronger. But polyester threads made today are much improved.

      The clothes that we buy are, by and large, sewn with polyester thread. That thread is not tearing the cloth. It makes sense to assume that our cotton cloth will be fine.



  4. I compose my old clothes as they are natural fibers. Into Big Bertha they go and a few months later when the finished compost comes out so does strings of looped thread….. they don’t use natural fibers to sew……


  5. Great information, Becky! Thank you. I have always been under the same impression about polyester thread. I may use it sometime in the distant future.


  6. I always press with a high cotton setting and my polyester thread doesn’t mind a bit. I usually use So Fine and Bottom Line. They don’t seem shinier to me, either.


    • There are levels of shininess and sometimes the difference is subtle enough that it doesn’t matter. Plus, when thread is sewn into a seam, shininess isn’t that big of a problem. It’s more an issue when you want invisible stitches, as in hand appliqué, or in EPP where all those tiny stitches can sometimes show on the front.

      I am still trying to track down actual heat resistance numbers on poly and poly/cotton thread. Recommendations vary, but the general consensus seems to be that high heat can weaken or melt a variety of synthetic threads, polyester included.



  7. When I bought my sewing machine from a dealer he said the worst thread to use is poly cotton blend. It chews the machine up worse than cotton. He has repaired more machines that use this. However I use cotton. I don’t plan on burying anything of mine. Lol


  8. Great to know! I find I use cotton with cotton material and Polyester thread with everything else. This is the same reason I try to match my needles to my fabric. It just makes sense. Thanks for sharing!


  9. In one of your responses you said you tried and tested just about every cotton thread out there. Would you be comfortable sharing which brand you prefer and why?


    • I’m currently writing a thread guide which is why I’ve been doing research. It’ll be out in a little more than a year, and it’s long enough that I can’t give a short answer to your question. What I can say is that we all need to look at and compare threads. I haven’t found any that are ‘bad’, but they are different from each other. One key thing to remember is the wt. number doesn’t mean anything related to thickness.

      Know how you want to use the thread and choose the ones that work for the task at hand. That should work for now, until the guide is out :-).



  10. Pingback: Polyester update… | Piece O Cake Blog

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