I would suggest getting pieces of plastic, either styrene or sintra, and trying to make the basic shape of the helmet. Although it might be a little hard if you only have that pic.
I agree, maybe vacuum forming might be your best bet, but it would be hard to put on, I wouldn't use latex because it is soft and holds a lot of imperfections that would kill your effect. maybe if you devided it up and made the top part plastic and from there down do latex so that way you can still move relatively comfrotably. But as stated earlier, it will be extremely difficult to make or even get advise on how to make it without more pictures.
I would work on making the best patterns you can from the basic shapes first. The helmet area and the two neck areas. I would either try to vacform those parts over shapes or I would use shaped sintra. With the sintra you could first create base shapes and then bend the sintra around the shape as it was hot from boiling water. You would probably have to do the upper helmet in a few joined sections or at least two sides.
To get in and out, I would connect the helmet and neck pieces all seperately with elastic straps. That way you could stretch it on/off and likely comfortably. Still consider ventilation.
You could glass it, but I don't have a lot of experience with that yet so someone else would have to chime in.
naw i use it on all my sculps for moulds along w/ a plaster backing to keep the shape. Works really well. Just maker sure you put in "cheese cloths" between layers of paintin on the latex to give it strength
naw i use it on all my sculps for moulds along w/ a plaster backing to keep the shape. Works really well. Just maker sure you put in "cheese cloths" between layers of paintin on the latex to give it strength