How much does a windshield sun shade actually lower cabin temperature?

Manufacturer claims of 20–40°F reductions are common, and verified-purchase reviewers on Amazon and Walmart broadly report a noticeable 10°F-plus drop versus an uncovered windshield. r/Costco commenters note the effect compounds with ceramic window tint. None of the sources in this dataset include instrumented lab testing, so treat specific temperature numbers as directional rather than precise.