The progression of bike helmets I have owned - at right, 16 years old (or so), in middle 8 years old, and the brand new one
The inside view of the three
The MIPS compliant LaZer Tonic helmet I just bought
Inside of new MIPS helmet - note the yellow inner liner that can move around
The Bicycle Helmet Safety Institute (aka helmet.org) says that Bell, for example, recommends replacing a bicycle helmet every three years - I think I've seen that elsewhere. Yes, what a wonderful world it would be for companies that make helmets if everyone followed that - but otherwise it makes little sense if the technology doesn't change.
In the late 1990s, I had a Specialized helmet that was mostly good for me since it was sized as a large (not "one size fits all") and I have big head. It was simply a chunk of Styrofoam (tm) with a blue plastic cover held in place with tape around the edge of it, some holes for ventilation, and simple straps. Space between head and helmet was provided by bits of spongy padding. It was good to put stickers on (the outside) but I think I outgrew that somewhere in my 50s.
In 2007 I bought a road bike that I guess was a ramping up in my seriousness (or something) so I decided I needed a new helmet - I found the red one made by Tirreno (which it seems is a Performance Bike house brand) in a large size on sale. It has been what I have used since. It looked sporty but I didn't find it terribly easy to adjust the straps, and recently the plastic ring that grips the wearer's head broke. The ventilation slots, while numerous, are narrower than the older helmet, which isn't so good. I also eventually realized it has a design flaw - towards the front there are slots that come together resulting in a parts of the helmet facing forward that could hook something hanging down from a tree (or whatever). This is in fact amazingly stupid (from a design perspective). Yeah, it is highly unlikely, but still - completely avoidable.
I have read about the MIPS helmet technology that is supposed to help prevent concussions by allowing the head to roll more easily in the helmet. Some people think this is baloney and maybe it is, but at least it represents an attempt at an advancement beyond basis protect for your head from a chunk of Styrofoam (TM). All the MIPS helmets are more expensive but I was able to find a LaZer Tonic (which apparently is intended for commuters) with MIPS from Bike Tires Direct for $75 on sale. It doesn't look like a road racing helmet (oh well) but it has good large ventilation holes, fits me well, and it is supposedly safer (maybe). I've ridden a few times with it; it seems good.
