True to size if you want a fitted look
"I got size S; ~115 lbs and usually S. The tank stretches throughout the time you wear it like most clothing, but it goes right back to that snug fit once it’s washed. So probably wouldn’t suggest sizing down for a more fitted look, definitely just true to size. Very flattering and comfortable, synthetic fabric downsides aside (but tbh it’s only synthetic fabrics that give this great of a snug fit). Get them on sale! Wish most of the colors weren’t out of stock."