Kerf cuts for tight foam curves

This page has safety advice that hasn't yet been checked by our safety reviewer. Treat it as general guidance, and follow your game's, venue's or product's own safety rules first.

Kerf cutting is a beginner-friendly technique for bending stiff EVA foam into smooth curves by removing thin slices of material from the back side.

When you need EVA foam to wrap around a rounded shape — a pauldron edge, a curved shin guard, or a helmet cheek — the foam naturally wants to resist and buckle. Kerf cutting solves this by removing a series of evenly spaced, parallel slots from the back (non-display) face of the panel, reducing the material that has to compress when the piece bends. The front surface stays intact and usually shows little or no sign of the cuts, while the slots on the back close up as the panel bends. To lay out your cuts, place the foam face-down and draw a series of parallel lines across the area that needs to curve. The spacing and depth of those lines both affect the final result: cuts set closer together or made deeper allow a tighter radius, while wider spacing or shallower cuts give a more gradual curve. Neither exact spacing nor exact depth is universal — they depend on the foam's thickness and density — so it is worth making a small test strip on scrap before committing to your main piece. Cut each line in one steady draw of the blade rather than sawing back and forth, which tends to tear the foam. Once the slots are cut, you can heat the panel gently with a heat gun, then press it over a curved form or against your reference object and hold it until it cools. The heat relaxes the foam and lets it settle into the new shape without springing back as much. If you skip the heat step, you can still bend the piece cold, but it may not hold the curve as well and could eventually creep back towards flat. Safety is important any time blades and heat tools are involved. Always cut on a proper cutting mat with the blade moving away from your free hand, and use a metal ruler as a guide rather than a plastic one that a slipping blade can ride over. Replace blades regularly — a dull blade requires more force and is more likely to jump off course. When using a heat gun, keep it moving and never hold it in one spot; EVA foam can scorch quickly and the fumes from overheated foam are unpleasant and potentially irritating. Work in a well-ventilated space, and younger makers should have an adult present for both the cutting and heating steps.