These will be latex, Vinchenzo (answered in the other thread, too).
Samaritan, if you can make the sculpt directly on the lifecast of a person, then the cowls should be a good fit. However, having a lifecast of yourself done can be expensive, so for this cowl I had John send me a bunch of measurements of his head and face. I used those measurements to sculpt an approximation of his head and face onto a purchased armature, then sculpted the cowl onto that. If I did it right, it should fit him well.
I've also sculpted several cowls using my own head as a guide (too claustrophobic to do a lifecast). Most of my cowls were made to fit my 24" head, and I've had good luck with them fitting others. If a guy's head was a little small for the cowl, it's easy enough to add a little padding for a better fit.
This is just how I do it, one of many variations. Definitely more than one way to skin that cat.