A bra with so much padding/push up that the extra volume alone is larger than the size of someone's boobs. Mattress bras are usually extremely thick and uncomfortable to wear.
"Dude, this chick I took home last night had MASSIVE TITS. I was so excited until she took off her mattress bra and she went from a DD to a B at best..."
by UrbanDictionaryDoctrine May 30, 2017