Victoria Secret Very

so my gf & i went to a Victorias Secret at the mall and i went inside with her for the first time. she was sorting through a bunch of bras on the racks and she kept picking out a few that she thought were cute. when she gave them to me to hold for her, i realized that the actual cup parts of it felt thicker, heavier, and like they were filled with some kind of gel substance. i thought that it was just a simple piece of fabric. can someone explain to me why this is? is it the same way with underwear? i didn't wanna ask her cuz i was afraid it would get awkard