Silver under roof thermal layer
Like a silvery sided cardboard under the aluminum roof skin. In pics it kinda looks like inside of the walls but if you look closely it is more shiny. It’s cardboardish - lays on the roof bows then the roof skin layer over top .
They call it “Therma Cool Ceiling Liner” - standard on a few brands of trailers
“ A Therma Cool ceiling liner is a thermal barrier and radiant heat reflector commonly used in enclosed cargo, utility, and RV trailers. It is designed to deflect solar heat, helping to lower the interior temperature of the trailer during hot summer months and improve overall climate control. [1, 2, 3]
Key Benefits & Details:
Temperature Reduction: Prevents the metal roof from radiating heat directly into the trailer, keeping the interior significantly cooler.
Trailer Compatibility: Often offered as an optional add-on or standard feature when purchasing enclosed trailers (e.g., for 5x8, 6x12, or 8.5x14 trailers).”