What does Spandex (PU) mean?

Derived from “segmented polyurethane”, it is broad term for man-made fibres and none for its ability to stretch well.

Heddels explains Spandex (PU)

Spandex is a synthetic fiber that was developed by Joseph C. Shivers in 1959 for Dupont. It was created as a replacement for rubber in women’s undergarments.

An anagram for “expands”, spandex is lightweight and extremely elastic, possessing the unique ability to stretch up to 600% and then return to its original shape. It is often used for swimwear and sportswear.

Spandex is also used in some jeans to improve their stretchiness, such as Cheap Monday.

Additional Resources

Cheap Monday denim with 2% spandex:

Source: stylehive.com