strips of vinyl along bottoms of windows, inside on side door panels

Any idea what the thin aluminum foil is for under these strips?

My guess is "heat" from the sun through the windows, the thin foil maybe prevents the strips from getting really hot in the summer sun???

any other ideas???

also, I recall awhile back asking about these strips and someone said to buy similar vinyl strip material, similar to them, cut them to the required length and install. Where would such vinyl strips be sold?