Because sizing systems vary and every body is different, finding a supportive and comfortable sports bra that fits requires some trial and error. But if you know your size and want to buy online, we spent more than 40 hours over the past three years, talking to eight experts, comparing hundreds of options, and testing 22 bras with 20 panelists (bands 30 to 42; cups A to JJ) to find some great sports bras.