Everyone, to the extent of their skills, available tools and ingenuity, used various, mostly construction materials to assemble the costume - insulation, glue gun, hiking mats, etc. In the past, a cosplay costume was literally made from the materials at hand.
Now there are special materials available for making parts. The most popular of these are Ava foam.
Eva
Eva is a very convenient material for making a variety of armor. The biggest advantage over other materials is its thermoplasticity. Eva bends easily when heated and holds its shape when cooled. Eva foam can be found on sale in different hardness and thickness.
But there are certain nuances - to cut eva correctly, you need patterns. When cutting, you need to consider the location of the edges and make the cut is not straight, but at an angle. The cuts, after gluing should be further processed with sandpaper. The surface of eva is porous, so before painting it is desirable to treat the surface with latex, to get a smooth surface. For painting and puttying it is desirable to use elastic materials, because the eva is still a little flexible.
Pepakura
Papercraft - as they call patterns (reamers) to make various elements of the paper.
Papercraft is not only fond of cosplayers, some just glue a paper model for a collection.
Usually pepakura is used as an inexpensive and easy way to make massive armor when there is no way to get eva foam.
First the paper model is glued. The paper is usually chosen with high density to minimize the risk of deformation of the model during further work.
After gluing the model should be strengthened. For this usually uses fiberglass and epoxy resin. When impregnating the paper model it is very important to make sure that the model geometry does not "hang". Usually, epoxy and glass cloth are applied in several layers.
3D Printing
Using a destiny 3d print models for making an entire costume may not always be feasible because of the cost. But in the manufacture of elements with complex geometry, small elements or high detail, it can greatly facilitate the task and save a lot of time. The 3D printer is indispensable for printing engineering, moving elements. It is very convenient when the model has a place for all the wiring and electronics and after assembling it is not necessary to puzzle over where to place everything.
But 3D printing also has its disadvantages. When making a model on the printer it is necessary to additionally process the model to obtain a smooth surface. If printed on a photopolymer printer, the cost of the finished product will be quite high. Large costume elements will have to be printed in parts and then glued together.