WOMEN'S LONG UNDERWEAR with NO FLY 400g/m2 Long Johns 400 Long johns are made of circular knit fabric, and have no lengthwise seams. A gusset in the back ensures optimal comfort. Cuffs are knitted in. 70% Merino Wool 28% Polyamide 2% Elastane Weight M: 328g The mid-layer 400 gm garments are used as intermediate layers to increase heat insulation between the base layer and the wind and water resistant outer layer. The mid-Layer garments are usually used at lower temperatures and lower activity levels.