It is very cheap.
The specific heat is 0.35 to 0.50 Btu/lb/°F, which is 1.5 to 2.0 J/gK. I do not think that is a high thermal mass. Also, the bubble insulation is inside the acrylic, so very little heat reaches the acrylic.
Bubblefoil on the inside? How does it stay in place? If you have any photos with the bubble foil installed I would like to see some.
Anyway, at R 1.1, it won’t make much difference except the heat won’t radiate out.