probably the polyester
yes
it is stretchy
Yes.
It's 58% polyester and 40% rayon, and is a knit fabric that has some spandex to make it stretchy.
Polyester is a very breathable material
Yes, polyester can be elastic. It can be combined with other fibers like spandex to create a stretchy fabric that has elasticity.
yes
Polyester is a material usually found in common things such as clothing and blankets.
The polyester material is made into threads, and the thread is then woven into cloth.
Materials (i assume you mean clothes of fabrics) are stretchy due to the amount of elastic in the fabric. More elastic means stretchier fabric, less elastic means it will not be as stretchy.
polyester