Not everything you read on the net is real. Inmates in my jails wore underwear, if they chose to. If it cane into the facilities it had to be white, no lettering. They could buy it from commissary if they wanted to. Bra as a weapon, more inmates would rather use the cotton from their socks to weave a garrote, easier to conceal and use.
I never heard of this. Undergarments are "jail issued" or if you have money you can buy the type they carry from the commissary and they must be worn at all times except when sleeping. Inmates cannot sleep in the nude. Men can sleep without a shirt however, women cannot but can remove their bra to sleep.