Alpaca is a warm light weight material for socks.  These socks fit well, a 43-46 for a size 10 W men's shoe.  It is hard to find a 100% Alpaca sock and my husband was very pleased with these socks.  They fit well with dress shoes as they are a lighter weight yarn but very warm for cold weather.  They are advertised as "fair trade" and we were pleased with this purchase.