I made my own. Used a gallon for exterior house paint from the scratch and dent aisle at Lowe’s, micro spheres from Wicks aircraft supply and then some of this
Paint Insulating Additive.
Much cheaper alternative and worked pretty well in my opinion. Could put a drop light (the ones that will burn your hand if you touch it for a split second) behind a test piece of metal (half painted, half not) and after 30 minutes I could comfortably rest my hand on the painted metal. I couldn’t say the same for the unpainted side.
I applied it to the entire interior and I think it made a difference (cant comment too much since I did a bunch more insulating at the same time) but interior of car was MUCH cooler afterwards.
FYI, their "special" application gun is basically an undercoat gun.
Dave