A warm sock without bulk? Highly breathable, but warm? Impressive materials and construction without a premium price? The Castelli Primaloft 15 Sock delivers all this and more, or less, as it were. The key lies within the name. A mixture of PrimaLoft® and polypropylene yarns keep your feet warm and dry. Simple as that. Primaloft offers some of the best light weight thermal insulation on the market. The material compacts without losing any of it's insulation properties and does not absorb water, maintaining it's capabilities at low temperatures.The polypropylene doesn't absorb moisture either, yet provides the yarn that creates the structure of the sock.

All the details are here: smooth toe transitions, reinforced heel, directional stretch arch compression, an effective level of compression to hold the 15cm cuff height up, and Terry-cloth construction bottom for extra loft and warmth. If you can't wear wool and struggle to keep your feet warm and dry while training in cool to cold temps, you will love this Primaloft 15 Sock.