This is a photograph showing different materials. Each sample is about 50 millimetres square and 25 millimetres thick. At the left is a piece of fluffy pink fibreglass wool. To the right is a pile of brown cellulose fibre pellets. To the right is a piece of brown dense rock wool. To the right is a piece of white expanded polystyrene. To the right is a piece of light blue extruded polystyrene. At far right is a piece of yellow polyisocyanurate foam with a thin sheet of aluminium glued to the top.