Down Sweater Sizing

Casey, I have a Patagonia down jacket and MB Down Inner UL Parka, both XL. Based on these I'd say these companies size accurately – I'm tall with long arms and both are near-perfect fits. I'd like a slightly longer torso but these pieces are intentionally shorter than other products these companies make. If your budget allows you might consider Nunatak, which is a custom shop – you can order extra or less length, more or less down, etc.

I have a Patagonia Micro Puff in Large, a Patagonia Down Pullover Hoody in Large, and a Montbell Ultralight Down Half Sleeve in Large. Both Patagonia pieces fit me fine with room for layering. The Montbell Half Sleeve barely fits me over just a baselayer. I have also tried on the Montbell Alpine Light Down Parka in Large and it had a trimmer fit than Patagonia. If Patagonia size Medium fits you in the micro puff I would go with large in anything from montbell.