My 4 mil double layered 4x4x8 grow tent. The inside is lined with styrofoam panels with the shiny finish on one side (don't know what they are but I got them at HD where the insulation is). Probably a 10 on the cheesy scale but the plants out grew my tiny closet and I had to make something to keep them in. One thing I am sure of is that it is light proof.
