Just about every Halo armour build out there uses the resin/fibreglass method. Here's an alternative method of constructing a sturdy armour, for those like me who:
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
First, find a pepakura file for the helmet. The one I used was from gamescanner.org, but it looks like the file is no longer available.
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
On its own, pepakura, even if printed on cardstock, isn't very suitable for papier mache, simply because the gooey papier mache strips will inevitably soak through the pieces, making it into one mushy, messy glob.
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
Using the spray adhesive, glue all the helmet pieces (except the visor pieces) onto the foil side of the foil wrap. Use the adhesive sparingly - the pieces don't have to stick completely onto the foil (ie loose, unglued edges are fine).
Wait for the adhesive to dry, then cut out the pieces with a knife and cutting mat.
Step 4: Cover the Pieces With Paper
Mix the PVA glue with an equal amount of water, and stir well. We'll use this to stick the papier mache layers on.
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
Assemble the pieces, three or four at a time, using masking tape. Trim off the papier mache around the edges if necessary.
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
Tear up some copy paper into small squares, and let it soak in water overnight. Then, drain out the water and mix in some undiluted PVA glue and cellulose wall filler powder. Knead, tear and scrunch the paper until it's the consistency of clay, adding glue and wall filler as necessary.
Step 7: Add the Details
Spread on the papier mache pulp with a spatula to form the finer details of the helmet. The amount of detail needed depends on which pepakura model you used, and how detailed you want it to be.
Let the pulp dry completely. This can take a few days, so be patient.
Step 8: Smooth Out the Outside
Mix some cellulose wall filler with water to form a thick paste (follow the instructions on the package). Use this to coat the outside of the helmet, filling and smoothing out all the irregularities.
Let the filler dry completely before proceeding.
Step 9: Paint the Helmet
Using your choice of paints (spray, brush, etc), paint the exterior and interior of the helmet with green and black paint.
Step 10: Make the Air Hose Thingies
Cut some a suitable lengths of plastic drain hose, and slice them in half. Paint them black and glue them onto the side of the helmet with a glue gun.
Step 11: Drill Holes for the Lights
On each side of the helmet, drill (or carefully cutout) holes for the lights. The green LEDs should sit in the holes snugly. Paint over the drilled out areas.
Step 12: Build the Light Circuit
Using a joule thief circuit, we can power all four LEDs with a single 1.5V battery!
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
Cut out a rectangle of yellow cellophane, just somewhat smaller than the laminating pouch you're using. Cut out a similar-sized rectangle of silver cellophane (or mylar). Place both sheets together inside the laminating pouch, and run it through the laminator. You'll get a shiny, yellow-golden sheet that will be used for 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!
And that completes the helmet!
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.