Great Question! The Lone Peak 4 Mid RSM is made to face the elements. As part of the Altra All-Weather Series (AWS) the RSM (rain, snow, mud) Lone Peak Mid features a brand new eVent® upper, which offers leading 100% waterproof technology and leading breathability providing maximum comfort and protection in the widest range of conditions. This new fabric material is also lighter and more durable than our previous version.