I have a few pairs of white arm coolers--I use them to avoid sun exposure. I don't know that they make me feel cooler but they definitely do *not* make me feel warmer.

But if you pour water on your arms w arm coolers on, you will definitely notice a delightful cooling effect--at least until they dry off!

I did a ride on the W&OD in late May on a brutally hot/humid day and at every water opportunity I stopped, poured water over my head and over my arms. Kept me going until the next water spot.