Montane mens prism jacket the most versatile piece of insulation in the montane range the prism is an essential piece of mountain clothing whatever the activity using 40g primaloft silver eco insulation throughout ensures that the prism is warm yet lightweight enough to be worn on the move in cool conditions used by mountain rescue teams across the uk the prism can be worn as a mid layer within any shell system or alone as an outer jacket in drier weather features versatile year ro