Polyurethane casting resin

A two-part liquid plastic that cures hard in a mould, used by cosplayers to reproduce detailed rigid props and armour pieces.

Polyurethane casting resin is a two-part material — usually labelled Part A and Part B — that you mix together in a specific ratio and pour into a mould. The chemical reaction that follows generates heat and transforms the liquid into a solid plastic. The finished piece can be sanded, drilled, primed, and painted much like any rigid prop material, making it popular for reproducing buckles, medallions, weapons, and armour details that need sharp, consistent edges. The mixing ratio and working time vary between products, so always read the datasheet for the specific resin you have bought before you open either bottle. Some formulas give you only a minute or two before the mixture starts to thicken, while others allow longer. Pouring too slowly or stopping partway through a pour can leave visible layers or weak seams in the cured piece. Colour and opacity also differ by product — some cure off-white or amber, which affects how you plan your paint layers. Because polyurethane resins release vapours during mixing and curing, working safely is not optional. Use a respirator fitted with organic-vapour cartridges, not just a dust mask. Work in a space with strong airflow — open windows and a fan directing fumes away from you, or ideally an outdoor area. Wear nitrile gloves and eye protection throughout, and keep uncured resin away from skin: repeated contact or breathing the vapour can leave some people with a lasting allergy. This is not a material for younger makers to handle alone; an adult should do the mixing and pouring. Check the Safety Data Sheet for your specific product; the manufacturer's guidance is the authority on hazards and first-aid steps. For LARP, cast resin pieces are hard props, not foam weapons. Many games keep rigid items out of combat entirely or allow them only as costume pieces. Your game's own rules and safety brief are the authority, so check them before bringing a resin piece to an event. Once you are comfortable with a basic pour, you can experiment with adding pigments, embedding objects, or casting into multi-part moulds for more complex shapes. Keeping notes on each pour — ratio used, room temperature, any bubbles or issues — helps you improve results over time and troubleshoot problems batch by batch.