from a bad blow..." Not exactly. Even motorcycle helmets don't protect from a direct blow over about 15 mph.
You have to define what you mean by a bad blow.
One kind of blow is just bad enough to knock you out or stun you, so you can't react to your situation. A shock absorbing liner helps, but it can be a liner that recovers. The shell should not be so stiff but that it initiates the shock absorption of the liner.
Another kind of blow markedly depresses most helmet shells, and can fracture or cave in your skull. That kind needs a stiff liner and a sacrificial, force absorbing liner. Makes for a thick, heavy helmet.
I can't see that ww helmet design has fully matured to confront these issues.
Fortunately, I found that cheap helmets like ProTec kept me from lasting harm through almost 40 years of moderate whitewater paddling. Now I have a Shred Ready t-dub, but I don't know if it's functionally much better. Sweet and Gath are worth looking at, too.
Fashion and false notions of effectiveness still infect the ww paddling industry. There is no Bell of ww helmets.
Heel and Pegpads™
Kayak & Canoe Outriggers
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