I seek a helmet, with a retractable face shield that actually covers the face.
I confess this is for a completely different sport. I am sufficiently confident of my fall practice not to worry about helmets while skating (then again, I've never tried a backflip or similar move), but whitewater boating is a completely different case, because bad things happen super-fast, including under poor visibility conditions, like under (muddy) water, and mobility is impaired by the kayak - I've twice hit my forehead on rocks, and once came close to drowning as a result.
At least one company
GATH makes a retractable face shield helmet sometimes used in water sports. Maybe there are others I haven't found. (You know of any?) Retractable is good, to briefly cool off, and it is absolutely essential in that sport to be able to drink water.
(There are many "full face" whitewater helmets - but they just have visors and chin guards - some of the face is uncovered. And gridded face guards are dubious - a stick could get caught in the guard, and hold one under water long enough to drown.)
But one on-line review says Gath helmets offer no padding. So maybe I should start with an oversized helmet, and add foam.
There have been many discussions on this board about foam to pad helmets for figure skating, some of which advocated rigid foams like polystyrene, which have to be replaced after every collision, but that is unsuitable for my purpose - in whitewater boating, there will inevitably be multiple impacts. However, unlike skate insoles, we aren't talking about hundreds or thousands of impacts, so super-minimal compression set isn't required, and there is no need for rebound. In addition, the foam will get wet, so open cell foams are probably out. OTOH, the helmet can be much more awkward, ugly and heavy than one might want for figure skating.
Could anyone recommend suitable foams, and perhaps how many inch(es) of foam would be needed? Assume the helmet is fairly rigid, so skull penetration by sharp rocks is not an issue, and that it will spread out the impact fairly well (I hope - which means that things like ball bearing drop tests aren't very relevant). I.E., I only seek gradual deceleration.
BTW, am I right that motorcycle helmets (some of which are much cheaper than Gath helmets) offer very poor ventilation and may in other respects be unsuitable? I assume they are pretty good at cushioning impact, and many do have retractable face shields.