Unfortunately, the only part of the underwear that is “leakproof” is the gusset part, as another reviewer pointed out. So, if the underwear shifts while you’re moving, you are bound to get blood through the part of the underwear that is not leakproof. I just used them today (light day) and I leaked through two different underwear after wearing them for less than an hour each. I regret spending so much money on them and buying the entire starter pack. The boy shorts seem better because they don’t move around as much. I contacted customer service but they didn’t really seem to care, and suggested I try using a diva cup with them, lol! Oh and the small size actually feels loose, more like a medium.