Single skin or single wall paint booths are generally made of walls and panels that are one singular sheet of steel. Dual skin or double wall paint booths are made of two layers of sheet steel that sandwich usually a non-flammable rock or mineral wool insulation in between. Look out! Some paint booths coming out of different countries like China have been known to carry styrofoam in between the panels which is cheaper to manufacture, but it is a code violation and can pose a potential hazard to anyone in the case of excessive heat or fire. It’s tough to know what is between the walls of a paint booth without ripping them open, but your manufacturer should be able to tell you this immediately. Styrene, polystyrene, eps are all names for styrofoam and they are all highly combustible and should never be used between the walls of a paint booth.
Single skin and dual skin paint booths perform very much the same. The heat losses from a single wall paint booth are minimal but the dual skin design of a paint booth is designed more so to protect the workspace outside the paint booth than to keep all the heat in for efficiency purposes. A dual skin paint booth keeps the area next to the paint booth cool and relatively undisturbed while the booth is in process. So if you have a tech working in a stall adjacent to the paint booth, he can work comfortably all day. If you’re in florida and the shop is already at 90 degrees, that tech will be alright to work. If you have a single wall booth and your paint booth is baking at 150 or 160, he will be miserable to say the least. The single wall booth will radiate its temperatures into the shop and the dual skin paint booth will not. In terms of efficiency losses, they are negligible between dual skin and single skin. Remember, you are rushing so much heated air through the cabin that the heated air is doing the brunt of the work. The radiant heat, while yes, technically leaving the system in terms of physics, will make no practical difference on how fast that job cures in the paint booth.