How much fluid do they hold? Customer Support February 09, 2020 09:07 Updated Follow Our undies absorb 2 tampons worth of fluid on their own. Add the optional booster for an extra 2 tampons worth. Related articles What does the booster do? What if I need to change my booster while I'm out? Do I need to wear a pad or tampon with them? How do I wash my Aisle undies? How do your period undies work? Comments 0 comments Article is closed for comments.