I can actually answer this! So the latex/rubber they used, while standard for Hollywood at the time, reacted REALLY BADLY to being doused in pouring water nonstop for an entire day of shooting. They ended up corroding, which caused them to stink really badly and glob together at the seams. The original plan was to hand out masks to various crew members on the final day of shooting as souvenirs, but the sopping wet, melting, rotting rubber got so gross that by the end of that shooting day they’d already thrown most of them out. Somewhere in a landfill are hundreds of disgusting, bloated, slimey Hugo weaving heads fused together into a nightmarish rotting amalgam :)