The Arcteryx Atom SL Vest provides superlight core warmth and can be worn either as a mid or an outer layer depending on the conditions and activity. When used as a outer layer and the weather takes a turn for the worst then a shell jacket over the top will be a perfect, albeit a very warm combination. The Atom SL Vest uses Coreloft insulation, a lightweight synthetic insulation that is very compressible and light but expands very quickly when unpacked. Coreloft is made up of thicker fibres than other leading insulation brands, which means it will not penetrate the outer fabric. The outer fabric is a soft and lightweight Ripstop Nylon which allows good breathability, features a DWR treatment providing good water repellency and also wind resistance. The side panels are Polartec Power Stretch with a Hardface technology, improving durability and weather resistance of the fabric. It is these Power Stretch panels that provide this vest with exceptional levels of breathability and mobility, but if it gets really cold or you slow down or stop it will be these areas where you will feel the cold first. Arcteryx Atom SL Vest Features Tyono 20 fabric with DWR finish Coreloft 60 insulation Polartec Power Stretch side panels with Hardface technology No Slip main zip Mid height insulated collar 2 zipped hand pockets Internal zipped chest pocket Adjustable hem Fit:Trim, hip length. Centre back 74cm (size M) Weight:160g Arcteryx Atom SL Vest