Next you need to prepare a spot outdoors or in a well ventilated area to put some resin on the outside. You want to work kind of fast depending on what resin you're using and the temperature your working in. I suggest working in small areas and letting it cure then go to another area and apply more. During the curing process the cardstock will become flimsy because you're getting it wet so take care in handling it. I would suggest leaving it sit where you do the resin stage. You will also want to pay attention to your surroundings as getting this on a floor will NOT be a good thing. Be sure to lay some newspaper/cardboard or drop cloth of some sort down before applying the resin. I suggest cardboard as it's thick and wont react to the resin.
Apply with a brush to get into all cracks and crevasses but be sure the brushes you use are either resin safe or ones you can throw away.
After the entire helmet has been covered and cured you should have something that is a lot more sturdy but still flimsy to a point and a shiny look to it..