Currently have two helmets, a Specialized road helmet I wear in the summer and a ski helmet I wear in the winter. I've started looking at extended coverage helmets and will probably buy one this spring as the road helmet is getting up there in age and I'm doing more gravel grinding and single track. I don't know just how much the foam becomes brittle and the cell structure starts to break down, but after a helmet has a few seasons on it, I'm usually ready for a change anyway. I usually keep my old helmet in a bag along with some cycling gloves and a few odds and ends for impromptu rides, but I gave my old one away a while back and haven't felt the need to replace the newer one yet.