large pieces of Used 25mm celotex type insulation (Malvern Link WR14)
Free - Malvern Link WR14 - listed on Trash Nothing
Used but still serviceable , gauge size by Wheelie Bin ! One is almost a full 2400mm x 1200mm sheet one roughly 1000mm x 1000mm the other is approx 2000 x 800mm https://trashnothing.com/pics/BVEZmtK