What is the shelf life of thread?
Due to higher grades of raw material and advanced processing technology, a top quality thread today will last much longer than thread which was made 30 or 40 years ago. Even the best quality cotton thread of a generation ago did not have processing techniques available to us today and it would probably be best to avoid using them. A top quality cotton thread (extra-long staple Egyptian-grown cotton, mercerized and gassed) manufactured today will probably be fine to use 50 or even 80 years from now. As for polyester thread, the color may fade over the years with exposure to sunlight but a quality polyester will last a lot longer than we will.
A tip to keeping your thread top notch: