I didn't get to have a fit of this one before I bought it. But with my Aero B-6 at a 38, I was easily able to figure out which size I needed for the D-1. I wanted something a little looser than my B-6. As mr_lits said, the B-6 has a slimmer fit and he's right. Definitely more form fitting to my body. The D-1 lets me wear another layer or two under it without problem (although I doubt I'll ever need to).