Spandex is a type of synthetic fabric that combines elasticity and spandex fibers. It is commonly used in clothing items such as leggings, swimsuits, and form-fitting garments due to its ability to stretch and return to its original shape.
So again, having Samus parade around in spandex in DOA isn't anything new, because she does that in Smash Bros, Other M, you name it (well, actually not in the Prime games so much). (nintendoworldreport.com)