The Geothermal Pants from Macpac have been designed with low volume layering with maximum warmth in mind. The robust and durable fabric is made to withstand the harsh elements and rough terrain as you hike your way through the wilderness. Theyre made from 100% recycled polyester to maximise warmth and manage moisture through the day. The flatlock seams ensure perfect skin comfort, making these thermal long johns ideal at retaining heat over long periods.