lining the inside of the new playhouse

I am looking through all the sites, ive found better insulation from screwfix direct, light and easy to put up £8 a roll its the silver stuff with bubbles in it, to line it tho looking at plywood, big jump in price and weight, need it to be sturdy but might need to move it so dont want to much internal weight was looking at this stuff which is what they use on the bottom of the play houses but not sure if its safe enough, it would be going over the insulation pinned to the internal frame of the house.

http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_secondid=9276289&fh_location=//catalog01/en_GB/categories<{9372016}/categories<{9372053}/categories<{9372281}/categories<{9392127}/specificationsProductType=length_2400mm