Nano, as in incredibly tiny. The teeny, tiny Primaloft® fibers warm better and compress smaller than any other synthetic fiber. So we stay warmer with less weight and less bulk. Plus, Primaloft keeps warming even when wet. Windproof, water-resistant and it weighs just under 10 oz. 100% recycled poly shell. XS(2), S(4-6), M(8-10), L(12-14), XL(16).