The mid-layer’s purpose is to retain the body’s natural heat, while still being breathable. Mid layers are anything between the base layers and the outer layers. Normal clothes can be considered part of the mid-layers, but generally we’re talking about things such as a fleece, which provide an additional layer of insulation. Adjust the number of layers on top so that they are appropriate for the weather conditions.
The colder it is the more mid layers required! Please NO JEANS/DENIM as they retain no heat