Fiberglass and polyester resin is a material often used for repairing boats and cars, but can also be applied to paper or cardboard in cosplay applications to provide strength and rigidity to a piece. This is perhaps my least favorite step in the entire process because of the awful fumes and messy nature of it. It is an extremely important step though, and with a few supplies and preparations it can go relatively quick and smooth.

My “toolkit” for fiberglassing a project consists of a good quality respirator (extremely important as this stuff is very bad to breath!), cheap disposable 1″ to 2″ paint brushes, newspaper to protect the work surface, 2-part polyester resin with hardener available at home supply stores (I use Bondo brand but others will work fine), fiberglass cloth cut into 1″ square pieces, rubber gloves to protect your skin, a small bowl and pieces of aluminum foil to line it (for mixing the resin), and a disposable stirrer (plastic spoons).

Typically in car and boat repairs, the resin is mixed with hardener and it gets “hot”. One would then paint on this goopey smelly mixture, apply pieces of fiberglass cloth (a heavy woven industrial fabric) and paint on more resin. As the resin dries it gets very hard and rigid and the woven pattern of fiberglass threads provides even more strength.

This technique can be adapted for use on paper to provide enough strength that a piece of armor can be wearable and hold up to further working and shaping. Before applying the resin, I needed to ensure the helmet would dry in exactly the shape I wanted. Once it is dry, attempts to flex the piece may crack it. I was particularly concerned with the two points that come together at the bottom of the helmet and almost touch beneath the chin. It was important that the points are symmetrical when viewed from the front, and that they come close to each other but don’t actually touch. To ensure this I glued a temporary “bridge” of cardstock that could later be removed but would keep the points in place while the resin dried.

Fiberglassing a piece like this is a two-step process. First, I apply a coat of the resin to the entire outside and let it harden (no fiberglass cloth yet!). I follow the manufacturers instructions and mix 10 drops of hardener per ounce of resin. I mix no more than 2-3 ounces at a time because it will begin to set up and be unusable in just over 5 minutes! Polyester resin creates a lot of heat once it has been mixed with hardener, and it is heat that speeds up the reaction and drying time. I have definitely noticed less working time with a batch of resin on a hot 90 degree day than in milder temperatures. You can also adjust the amount of hardener you add in order to speed up or slow down the reaction.

Once the entire piece has been coated on the outside with resin, it should have the appearance of a “greasy napkin”. This is the sign you have applied enough resin as the paper is soaking it up. It will actually be dry, hard, and able to be handled in about 30 minutes, but I still allow a full 24 hours to get full strength before moving on to the next step.

The second stage of this process is to apply the small pieces of fiberglass cloth and more resin to the INSIDE of the piece. It is the cloth that will provide most of the strength in the final piece, but it has an uneven bumpy surface when dry so it is best to apply it to the inside where it won’t affect the finished surface. I used a spray adhesive glue on the inside of the helmet, then lined the entire inside with the little cloth pieces, trying to overlap their edges slightly for added strength. Once the cloth is in place I mix up another batch of resin as before and coat the entire inside of the piece. Make sure all of the cloth pieces are soaked with resin and none of the threads are still dry (but be careful not to over-brush as your cloth may start to move around). Again, I allow this stage to dry for a full day before moving on.

Once all the resin has fully dried things start to get really fun! The piece is now significantly heavier from the resin weight, and it is also much stronger and feels less like paper and more like a sturdy prop. Be careful at this point because any stray or overhanging threads of fiberglass will be very sharp–I had to resist the urge to put it on yet because my head would have been pierced in several places!

Stay tuned, my next post will detail sanding, filling, shaping and smoothing the helmet in preparation for painting.

-J