Here's how to make a low cost costume helmet using cardboard. Helmets are usually one of the hardest and most expensive parts to make for a cool Halloween costume so here's a simple method I use. The methods I describe can be used to make almost any kind of helmet but I'm showing how to make a Star Wars Boba Fett helmet as an example - I have an instructable for the rest of the Boba Fett costume here:
The templates provided are used by permission from The Wizard of Flight via the Dented Helmet- the definitive Boba Fett costume resource-thanks Alan! The templates are designed to be printed on 8.5" x 11" paper.
For more great scifi costuming templates check out SPC -there's a lot of fantastic patterns there!
You'll need some cardboard sheet- about 1/16 inch thick material works best. Use the kind that looks like paperboard- corrugated cardboard won't work. The kind I used is called newspaper board and it comes in 30"x40" sheets. It is manufactured by Crescent as well as Arches and is sold at craft and picture framing stores. Crescent shows it on their website as Grey News Mounting Board:
Some people have reported that Ram Board also works extremely well.