These ultra-soft breast shells from Philips AVENT are meant to be worn inside of your bra to protect your nipples from chafing and collect excess breast milk.
The ventilated shells protect sore or cracked nipples to help them heal more quickly. The gentle pressure they apply helps to relieve engorgement and the holes allow air to circulate.
I would wear one of these while Breastfeeding to capture milk that leaked out of the non-nursed breast. I could then pour into a storage bag and store it in the freezer for later. It was less wasteful than just soaking up the excess with a bra pad. I don't think they would be very comfortable to wear all the time mind you.