The Compressor Vest is considered a heavyweight mid layer piece or a super lightweight outer that gives superb freedom of movement whilst on the crag. It allows your arms to work hard & not over heat while it keeps your core protected from the cold winds. The Helium 30 outer fabric is highly windproof protecting the nice warm air that is trapped within the Prima Loft insulation. The Compressor Vest packs into its own pocket & can be attached to your harness using the stitched in crab loop, so when you do get a bit too warm you can stow it away but still have it close to h&. Helium 30 outer is exceptionally lightweight & windproof Prima Loft GOLD insulation [60g with 40g arms & side panels] Quilted body construction 2-way YKK moulded centre front zip 2 zipped hand warmer pockets Napoleon chest pocket Dual tether hem drawcords & non-absorbent stretch cuff binding Packs into hand pocket with karabiner carry loop For all you kit geeks out there, the links below will take you to Mountain Equipments Information pages where they will explain this jackets different fabrics, fills & constructions techniques in greater detail. Helium 30 Prima Loft Gold (Formerly known as Prima Loft One) Dual Tether Hem Drawcords Most people are scared to wash their outdoor jackets but like all equipment it does need to be maintained. It is actually really easy! Feel free to give the shop a call from 09:00 until 17:30 Monday to Saturday (19:30 on a Wednesday), as we are always happy to help & give friendly advice. Or if you are reading this outside our normal opening hours here is a useful link to Trekitts recommended product for washing & caring for kit. Nikwax Tech Wash Nikwax TX-Direct I hope this helps.