Contact cement

A strong adhesive used to bond foam, fabric, and other costume materials permanently, popular with cosplayers for joining large surfaces.

Contact cement is a brush-on or spread-on adhesive that works by coating both surfaces you want to join, letting each coat become tacky, then pressing the two sides firmly together. Because the bond forms almost instantly on contact, you get very little time to adjust your pieces once they touch — so careful alignment before you press is essential. It is especially popular for bonding EVA foam because it creates a flexible joint that moves with the costume rather than cracking. There are two main types you will encounter: solvent-based and water-based. Solvent-based contact cement generally produces a very strong, fast bond and holds up well to heat and flexing. Water-based formulas are less harsh to work with and clean up more easily, but bond strength and flexibility vary between brands, so check the product's own instructions and test on scrap material first. The right choice often depends on your workspace and how sensitive you are to fumes. Safety is especially important with solvent-based contact cement. The fumes are strong, flammable, and harmful if breathed in over time, so you must work outdoors or in a space with active ventilation — open windows alone are rarely enough. Wear a respirator fitted with organic vapour cartridges, not just a dust mask, plus nitrile gloves and eye protection, and keep heat sources and open flames away from your work area. Younger makers should have an adult present at all times. Water-based versions are less hazardous but still benefit from good airflow. Read the safety data sheet for whichever product you choose before you open the tin. Application technique matters a great deal. Most makers brush a thin, even coat onto both surfaces, wait until the adhesive is no longer wet but still tacky, then bring the pieces together with firm, even pressure — a roller or the handle of a tool can help seat the bond. Applying too thick a coat or pressing too soon are the most common causes of weak joints. Some builders apply two thin coats to porous materials like foam to get a better seal before the joining step.