I figure that if and when the time comes for my helmet to protect my noggin, I want it to work as well as it can.

So I go ahead and replace it every 18 mo or so.

I do NOT "bang it around", in fact I take good care of it. The styro can only compress once - and then it's done. Some folks beat em up: throw them in the back of the truck, toss them around - I try to take good care of it.

I stick with the 18mo interval because the price of last year's models isn't bad, and by then, my pads are going south, the straps are often a bit frayed, I've sweated hundreds of gallons of salt water onto it, and it gets baked in the salty solution in the garage in the summer

cheers