Built to tame the Mountains, The Kaibab 300 was designed and crafted as a universal core insulation layer using Superfine Merino wool. At 300 grams per square meter, the Kaibab 300 is a powerhouse at maintaining core temperature and is designed to be layered against the skin with the flexibility to layer independently over a base layer shirt. No other fabric breathes like Merino wool which is why Merino was the clear choice in constructing this incredible base layer.