the walls are lined with a special 2 sided visqueen called panda film...a 10' by 100' roll is around $70-$100..the white side will reflect the light and heat rather than absorb it...there shoud be no worries on melting it...ive had a room hit upwards of 100+ when a fan went out and experienced no problems with the film...the plants got a little pissed but they came back........