Merino fabric beefed up by Outlier, can't figure out the exact model. "midweight merino pullover halfway between a sweater and a sweatshirt. More structured than most sweaters, more breathable than most sweatshirts." - sounds about right It might be the Warmform, it definitely has: - Collapsed waffle knit - 65%17.5 Merino Wool - 27%Nylon - 8%Elastane - Highly breathable and moderately durable - beautiful combination of soft performance, ruggedness and structural snap The fabric is mostly Merino, with some synthetics added. Overall the fabric is pretty heavy and feels super durable. Fits large, loose and roomy with a nearly 24" P-P measurement.