This a Robb's custom-fitted brace. Until he is stronger, this will be his "external spine." It will offer support when he is sitting or standing.
He was measured for this on Wednesday, and it was delivered on Thursday morning. It is made of heat-moulded plastic, and fits perfectly. It has tiny holes in it, so his skin can breathe. This photo shows the front side. The black part holds the brace in place, so that it doesn't ride up.
Right now, he wears it during some of his physical therapy sessions.