Basically...WOF templates modified, foamboard, and styrene sheet....an iceball mold... plastic cup..etc etc... mold the parts cast them, refine, remold...etc etc You can see most of the process here:
Scroll down to post #24....the first attempt got scrapped...
http://www.thedentedhelmet.com/f20/...ratch-build-2015-updates-45641/?highlight=DVH
Here is the link to the templates:
http://www.thedentedhelmet.com/f20/...ck-patterns-7559/?highlight=jetpack+templates
I did mod them a bit and then modded the pack itself after the first cast... but the basis is 100% WOF