The sizing for this jacket cannot be compared to the Slim Fit N-3B as the two jackets have different fits (core vs standard) and the variations between sizes differs between the two styles. When determining your size please consider whether you will layer under the jacket and if you prefer a more fitted lookThe N-3B parka is one of our warmest; suitable for sub-freezing temperaturesThe 100% nylon outer shell, polyester interlining and faux fur-lined/trimmed hood make this Snorkel parka optimal for staying warm & dryOur cold weather parka also has a full-length storm flap and inset knit cuffs for additional protection against the elementsThe USAF N-3B parka is tough, with reinforced elbow patches, in addition to an adjustable take-up strap/draw cord in the hood