A mid-layer is a type of clothing designed to provide insulation and warmth while allowing moisture to escape. It is typically worn between a base layer, which is close to the skin, and an outer layer, which protects against wind and rain. Common materials for mid-layers include fleece and down, making them lightweight yet effective in retaining body heat during outdoor activities like hiking or skiing. In outdoor gear, the mid-layer plays a crucial role in temperature regulation. For example, when wearing a hiking jacket, a good mid-layer helps keep you warm without overheating. This balance is essential for staying comfortable in changing weather conditions.