DuofoldWomen's Mid Weight Wicking Thermal Shirt

Cuddl Duds are 54% polyester, 46% cotton - these are 60% cotton. Do these having more cotten make a big difference in keeping warm??

Does this top run true to size?

Is this single or 2 layer underwear?

Would this top be good for hiking/backpacking? just wondering how good the moisture wicking is.