just wanted to know if a 1200x2400 sheet of 75mm rigid fibreglass would be able to stand up by itself (leaning on a wall at a slight deg.)? Do they normally need frames of sorts to mount them on in corners or could I just lean it in a corner to test different placements?
No, it's not that rigid; that large a sheet of 3", depending on density, would probably stay as straight as a piece of 3 or 4 mm paneling under leaning conditions... Steve