This thrummed beanie is the hat for the coldest weather. The thrums and the double layer with the fold-up brim around the ears will keep you incredibly warm! This hat is constructed in continuous rounds in one piece, with thrums added on the first half.

Special stitches
There is a wonderful tutorial for adding thrums on KnitPicks by Daniel Kennon available here: https://tutorials.knitpicks.com/learn-to-crochet-thrums/