Longman Dictionary of Contemporary English
Wikipedia
A padded cell - or Personal Safety Room - is a cell in a psychiatric hospital with cushions lining the walls. The padding is an attempt to prevent a patient from hurting themselves by hitting their head (or other bodily parts) on the hard surface of the walls. In most cases, an individual's placement in a padded cell is involuntary.
A padded cell is sometimes colloquially known as a "rubber room", seclusion room, time out room, calming room, personal safety room among others.
Usage examples of "padded cell".
I was even afraid to look out the open door, afraid they would think I was trying to escape, and then I would be put into a padded cell for sure.
They opened up the padded cell and there he was, dead, and turning black already.
His heart jumped against his ribs like a maniac in a padded cell for one eye was sky blue and the other violet flecked with gold.
The whole passenger compartment could become exactly that - a padded cell - in the event of accident.
A little while after she'd woken up whole and well, alone in that padded cell, a woman wearing a black uniform had come and escorted her to a bathroom with a shower, given her a rolled towel that contained a toothbrush and soap, and told her to wash.
Must have spent what there' d been of his life in some padded cell or a hospital bed, something like that.