How does bruce baners pants stay on when he changes into the hulk?

Since bruce baner waiste size is typically around 32' and his pants size is the same, but when changes the "Hulk" his waiste size increases to 60" -"80 inches which would cause his pants to rip off. And, since their is no elastic pants in existience that stretch that far, his pants would rip off. So, how is pants still on? Funny!!!