The Patagonia Nano Puff Vest earns its place in a layering system by doing exactly one thing well: holding heat at the core while keeping arms free for full movement. The recycled ripstop shell and PFAS-free DWR finish work together so the vest pulls duty as a midlayer on cool approaches and as a sealed layer when the shell goes on top. What Our Gearhead(R) Experts Are Saying:"I wear this under a shell on high-output ski days because the PrimaLoft Gold keeps my core warm without trapping heat when I'm moving hard up the skin track."