Diva cup

How does the diva cup work exactly, in terms of leaking. If it can be used for up to 12 hours straight but you've got a really heavy flow. And it's supposed to make a tight seal so it doesn't leak..

I might not be imagining it correctly in my head, but since it's a cup and it's sealed, shouldn't it be nearly impossible to leak? Like even if the cup is technically full, how does the blood leak thru the plastic. Cause apparently it doesn't just work like a plug 🤣

I don't understand why it leaks I'm sorry. I don't wanna deal with it leaking every hour and I don't have pads