I have no idea but I’m guessing it’s velour..... copy and pasting what I seen on the innerwebs
Velour is a knit fabric with a natural stretch, while velvet is woven, and therefore does not naturally stretch. Also, velour is most usually made of 100% cotton. Velour gained popularity as a fabric made for clothing in the 1970s. Prior to that, velour was usually used for upholstery
Might find it in a adidas tracksuit from the 80’s (jk)