Random Friday afternoon Science Question!

[Dr. Z]

Originally Posted by LeperousDust

You'd be watering down the most effective, so at best 8, at worst something between 4 and 8.

This man speaketh the truth, from a logical mathsy POV.

However, as laymen we know that the delivery method is the cream which obviously mostly evaporates or has the moisture content absorbed into the skin leaving the protecting agent behind. If the mechanism for this was to leave a layer of UV-filtering chemicals on the skin then applying in two layers would allow you greater protection (on the assumption that the second application did not damage the first layer in any way).

To summise: Stop being a pov and go and buy better sun cream!