Well you got me questioning my information. Found the following on the superiorthread site and probably explains why I thought as I did. I was told that threads don’t last in a sewing class many years ago and have always been concerned. I think I might give my thread a test and then do some replacing as necessary when I see my regular sewing supplies again.
I took a class at the Singer store while in junior high and made a lot of my clothes for many years – I even did a jacket with bound buttonholes while in high school. Maybe I’ll put sewing on my when we finally get back in the house list. It would certainly be easier than finding things on the store racks. And I think my information actually came from a class later when I was told to keep moisture in it and store in freezer used
From superior threads:
A. A good quality thread that is produced today will last much longer than thread which was produced 15 or 20 years ago. Even the best quality cotton thread of a generation ago did not have the advanced processing techniques available to us today and it would probably be best to not sew or quilt with old thread that exists today.
However, a high-quality cotton thread that is manufactured today, like MasterPiece and King Tut, will probably be fine to use in 40 or 50 years from now. Why will threads that are manufactured today last longer than threads manufactured 20 years ago? The difference is due to the advancements in spinning, dyeing, and twisting technology and the evolution of genetic engineering better cotton plants. Because cotton is a natural fiber, it will degrade over time. A good test to check whether or not the cotton threads you have been given are OK to use in your machine is to hold about a one foot section between both hands and pull apart. If the thread snaps (you should feel a nice, crisp break), then it is OK to use. If the thread just separates and pulls apart easily (think of pulling a cotton ball apart), we don’t recommend using it.
As for polyester thread, the color may fade over the years with exposure to sunlight, but there is no evidence that the thread deteriorates like cotton threads, so it’s safe to say that synthetic fibers will last longer.
source: superiorthreads dot com
(Note – I saw other posts that said it was no good if it did snap. I personally think the superior threads response is more accurate. CR)