The following pictures show the flexibility under pressure. The crest is under the same amount of pressure in the first image and the second. It returns to the original shape, after 30-50 crushes. It has been stepped on, sat on and struck with rattan weaponry without ill effect. I think that several actual combat sessions would leave it looking a bit scuffed and dirty but if it were attached in a way that allowed it to detach under a strike, I suspect it would hold up to numerous fights without major problems. If it were attached permanently, several combat sessions could cause ripping in the foam.
The base is shown in the final image. It shows an inverted domed base.
I am playing with the idea of putting a domed leather cap on the helm first, attached by lacing to 4 holes in the crown. There are some holes seen in the crests of a couple of extant helms though, admittedly, they don't seem to be common. I am hoping to attach the various helms to a matching nestling domed base, so they can be altered.
This style is obviously a modern substitution. It is, however, an easily accessible option for people who just want to buy a crest that looks good. Over all, it seems a durable, safe design.