I wrote a post about polyester thread on August 17 in which I said that the research I could find indicated that polyester thread probably doesn’t degrade any faster than cotton thread. There’s more to the story…
#1
I still can’t find any research specific to thread longevity. My husband tells me that if absolutely no references to research show up in a google search, there probably are none to be found. Thread makers do post information about their own collections of thread but that’s not the same as academic research.
The one study I did find (click here to read it) compared the biodegradability of cotton vs. polyester fabric in a compost pile. Cotton fabric degraded quicker and more thoroughly than polyester fabric which indicates that polyester thread should last longer, right?
My husband, Steve, is a field biologist who teaches invertebrate biology. When I brought this study up at dinner recently he said that decomposers (the bugs and microbes that live in compost) would recognize cotton as food and happily eat it. They don’t necessarily recognize polyester, a petroleum product, as food. Of course cotton degrades faster in compost (he didn’t add ‘duh’, but I’m pretty sure he wanted to).
#2
On August 28 the New York Times published an article entitled “These Cultural Treasures Are Made of Plastic. Now They’re Falling Apart.” Click here to find the story. It’s definitely worth reading.
I read a similar story years ago in the Dallas Morning News but I didn’t save it and have not been able to find it. I was beginning to doubt my memory. It turns out that what I remember from that article is still true… Tupperware, spacesuits, and plastic artifacts of all kinds are degrading.
Now what?
There are all sorts of plastics and they degrade differently. Again, I can find no specific information on polyester or synthetic threads.
I don’t believe that polyester or synthetic threads are inherently bad, or that we shouldn’t use them. There are many times when a polyester thread is the best choice. That said, every time we choose thread for a project, we weigh a variety of factors… this is just one more thing to keep in mind.
Piece O Cake Blog 
A few years ago I made a small wall hanging and machine quilted it using some ‘vintage’ cotton thread from a wooden spool that I had inherited from my mother. Needless to say, the thread fell apart after I quilted it and was very easy to pull out. I had to pull it all out and rebuilt the wall hanging. I’ve used modern, new cotton threads since then.
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Old thread is tempting but it’s probably a bad choice for actual sewing.
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Good information!
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I believe poly threads require a cool iron. Glide brand threads recommends a cool iron for its silk threads…My conclusion is to get your serious ironing on cotton fabrics completed before adding poly or silk threads.
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It makes sense to follow manufacturer’s guidelines. Amazingly enough, there doesn’t seem to a consensus on iron heat when it comes to synthetic thread and there’s no hard data as to how hot is too hot. It’s probably good to be cautious heat-wise.
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Years ago one of the reasons given for not using polyester thread in quilting was that it “cut” the cloth fibers over time. That wasn’t mentioned by you and I thought that curious.
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As long as you match the strength of the thread with the strength of the fabric, it’s not a problem. Almost every garment you own is sewn with polyester thread and your clothes are not being cut by the thread. Luckily, that’s a notion that we can let go of :-).
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