The outer layer is another important layer because it provides protection from the elements. The layer needs to be both windproof and waterproof. The mid layer without the outer layer will not be as effective because it is exposed to both wind and moisture. If the piece is windproof, heat will better stay trapped under this layer. This layer should be worn loosely, in order to accommodate the changing mid layers. This piece should have the ability to be worn in all seasons. That is why it is important for it to have plenty of room. In the winter it can house many mid layers and in the summer time it fits loosely and will have a greater amount of breathability. Ventilation is important during high energy exercise in order to release excess heat and water vapor and sweat.