When inserted correctly, the cup shouldn't leak if it’s not completely full (and presuming you have the right size). The key to a leak free period is to make sure the suction seal is created and that the cup is completely unfolded inside you. After inserting, you should pinch the bottom of the cup (or insert your index finger alongside the cup) and slighlty rotate it until it unfolds without any dents around and until it doesn't move downwards when pulling the stem. This is how you know the suction seal is in place. For more tips & tricks check out our guide 'How to Use a Menstrual Cup' here.