I have only one helmet (really cool Shoei one which I love!) currently and I commute everyday and also weekend rides. Wondering if I need a second helmet to rotate, especially in summer when I will be sweating more. The helmets are expensive so I don't want to have 2 just for the sake of it. Also, I read somewhere that helmets only last 5 years if not dropped or crashed because the foam deteriorates in that time. Opinions? Also, if I do get a second one, is it a good idea to get the same model to share visors etc? Thanks everyone.