Mid Layer is a fairly ambiguous term, but for the purpose of our layering system, it’s something you wear over your base layer when the condition’s call for extra warmth. Usually this will be in the form of a Men’s or Women’s fleece, such as a 100 weight or 200 weight in traditional terms, or a merino mid layer equivalent. Generally you will want your mid layer to feature a zipper, be it half-length or full-length. A half zip will be less bulky, but a full zip offers more venting options. Which you choose will boil down to personal preference and the activities you’re buying it for. Mid layer items are also often worn alone (over your base-layer) on shorter trips and in mild weather conditions. The pieces you choose should be comfortable, lightweight and more robust than your base layer clothing.