I bought this along with the Capilene 2 Bottoms. My initial thought when buying was it might be heavy because I own Merino wool sweaters. I was dead wrong. This shirt is feather light, breathable, and unbelievably warm!I'm 6'3" and 195 lbs. and bought an XL so I could use it as a layering piece with a wicking T-Shirt underneath. Check the size guide to make sure you get it how you want it fitted.Bottom line: I live near Chicago and will no longer buy Under Armour or Nike for my baselayers. Patagonia is the bee's knees and Moosejaw got this to me in 4 days with ground shipping. Talk about the cat's pajamas.