The Atomic Treeline PrimaLoft Jacket M is a super versatile midlayer – featuring PrimaLoft insulation on the inside and water resistant Pertex Microlight on the outside. These high-tech materials work together to keep you warm and dry without adding weight or bulk. And while we’ve designed it specifically to be thin and lightweight, we’ve made sure it’ll withstand the wear and tear of everyday use – and keep going for years.