Hi Peter!
Thank you. I know what you are talking about. I worked once a a signmaker, and we used some of it. It was "new" at the time.
In 2006, I sculpted an entire 1/1 street rod body for a customer (see pix below), out of HD40 insulation foam that the factory sliced in huge blocks from the 49 X49X97 raw castings. Lots a foam particles left over, but it was later coated with latex paint to create a barrier, and laminated over with fiberglass. Quicker to produce a one-off body like that than making molds.
Happy new year to you, and many creations in 2023!
CT