These thicker 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.
Long Johns are made of a circular knit fabric, and have no lengthwise seams. A gusset in the back ensures optimal comfort. Cuffs are sewn in. With fly.

Materials: 

60 % Merino wool
25 % Polyester
13 % Polyamide
2 % Elastane