Soft shell is a family of cloth you wear in order to keep you warm. above the soft shell you wanna use a hard shell like a double layer gortex jacket and pants. Cloth made of fleece belong to the soft shell family. For me, when up on the mountains, I'll wear a soft shell above my base layer. I will not go for fleece though, because it doesn't breath, that's why it's a good insulator, and it'll trap my sweat. Many other artificial fabrics like polyester breath better and keeps you warm as well.