a) lack a large enough garage or home workshop to safely apply resin and fibreglass, and
b) are sensitive to the chemicals used in resin and fibreglass
This method uses papier mache, which, if done properly, gives something rock solid (or more so than cardboard, anyway).
For the helmet:
Lots of paper, 70-80 gsm (eg normal copy paper and brown kraft paper)
A roll of paper backed foil wrap
White PVA glue, 1 litre
Cellulose wall filler (or spackling paste)
Yellow cellophane paper
Semitransparent silver cellophane paper (or silver mylar)
One hot laminate pocket (A4 or letter)
One plastic washing machine hose
For the helmet lights:
4 green LEDs, 10 mm
One ferrite toroid
One npn transistor (2N2222, 2N3904, or equivalent)
One 1k resistor
One 1.5V battery holder
One 1.5V battery
Green acrylic paint
Black acrylic paint
Total cost of the above is $50 or less, depending on your scrounging skills.
A sharp blade for cutting paper
Containers to hold glue and pulp
Paintbrushes (if you're not using spray paint)
Step 1: Get the Pepakura Files
But there's more here:
Check out the tutorials on how to scale the helmet (if necessary), then print the pieces on normal copy paper.
Don't cut them out yet though!
Step 2: Preparing the Pieces
So we borrow a trick from origami - the tissue foil laminate. Or in this case, the paper-and-foil laminate. What we do is to first glue the pieces onto some foil wrapping paper, the sort that is metal foil on one side, and paper on the other. The metal foil is malleable, yet holds its shape even when wet papier mache is slopped onto it. This allows us to layer on the papier mache onto the pieces without everything falling to bits.
Use wrapping paper with thicker foil and paper layers.
If you can't find this kind of paper, you can make your own by gluing thick kitchen aluminium foil to some brown kraft paper.
Step 3: Glue and Cut Out the Pieces
Wait for the adhesive to dry, then cut out the pieces with a knife and cutting mat.
Step 4: Cover the Pieces With Paper
Have the kraft paper and copy paper ready.
Soak the kraft paper in the glue mix, and tear them into small squares (~ 2 cm). Make sure the paper is entirely soaked, and not just coated on the surface. Wipe off excess glue from the paper squares, and then paste them onto the reverse side of one helmet piece (ie the paper side of the foil wrap). Smooth out each paper square, pressing out air bubbles and excess glue. It's fine if the paper squares extend past the edges of the piece.
When the piece is completely covered with kraft paper, repeat the process with copy paper.
Let the pieces dry in the sun, but not completely - bring them inside when they feel about as pliable as leather.
Step 5: Assemble the Pieces
Add two more layers of papier mache on the inside, where the pieces join up.
Allow the papier mache to dry completely.
Assemble the next three or four pieces in the same way, then repeat until the entire helmet is done.
When the entire helmet is assembled, add two more layers of papier mache both on the inside of the helmet, and on the outside, and let it dry completely.
Step 6: Prepare Some Papier Mache Pulp
Step 7: Add the Details
Let the pulp dry completely. This can take a few days, so be patient.
Step 8: Smooth Out the Outside
Let the filler dry completely before proceeding.
Step 9: Paint the Helmet
Step 10: Make the Air Hose Thingies
Step 11: Drill Holes for the Lights
Step 12: Build the Light Circuit
There's already many great instructables and other online guides on how to make a joule thief (here, for example) so I won't go into too much detail here.
The LEDs are wired up in pairs. The ferrite toroid and resistor is stuck to the side of the battery case, and the whole assembly is glued to the back of the helmet. The wires leading to each pair of LEDs naturally should be long enough to reach the holes. The wires leading the switch should also be long.
Glue the LED wires along the sides of the helmet, and the switch to a convenient place at the base of the helmet.
Insert the LEDs into the holes drilled earlier, and glue them in place.
Step 13: Making the Visor
Trim the borders of the sheet to fit the helmet, and glue the visor in place with a glue gun.
Step 14: You're Done!
This helmet build took me about 20 hours, spaced out over four weekends. This does not include overnight drying times for the papier mache though.
The rest of the armour can be built in a similar fashion.