Maybe this is common knowledge? A cheap plastic shower cap fits perfectly over a helmet and visor. It fits tight and does not interfere with the straps. It blocks the wind and rain. Some air gets in under the helmet rim, so it is not too hot and there is not much condensation. The little condensation is way up above the head, over the helmet and on the shower cap. I don't know yet how long they last, but for 99 cents US, I'm risking the investment.