Hot-wire foam cutting is a way of shaping foam by melting a clean line through it with a thin, electrically heated wire. Instead of cutting the foam mechanically (which tears, crumbles and makes a mess), the wire heats up to a few hundred degrees and the foam simply vaporises in a narrow path right in front of it. The result is a smooth, sealed, dust-free surface that no knife or saw can match.
It is the standard technique for working with expanded and extruded polystyrene — the white "bead" foam (EPS) and the coloured insulation board (XPS) — as well as several other plastic foams. Model aircraft wings, architectural mouldings, theatre props, sign letters, packaging inserts, surfboard cores and insulation parts are all made this way.
How it works in one sentence
A resistance wire (usually nichrome or stainless steel) carries a current; the current heats the wire; the hot wire melts a thin channel through the foam as it moves; the foam falls away on either side of the path, leaving the shape you wanted.
Why a hot wire instead of a blade?
- No dust, no crumbs. The foam vaporises rather than shattering into static-charged beads that stick to everything.
- A sealed, smooth finish. The melt re-fuses the cut face into a slightly glazed skin that needs little or no sanding.
- Very low force. The wire barely touches the foam, so thin and delicate shapes do not get crushed.
- Long, straight, accurate cuts. A taut wire stays dead straight over a metre or more, which a bandsaw blade cannot.
- It is cheap. A length of wire, a power supply and a frame will cut foam better than machines costing far more.
Manual vs CNC hot-wire cutting
The simplest setup is a hand-held bow with a wire across it — great for straight cuts and freehand work. A CNC hot-wire cutter adds motors that move the wire along a programmed path, so it can repeat complex profiles perfectly every time. Most interesting shapes (aerofoils, tapered wings, twisted columns) need at least two motorised axes; truly 3D parts need four or five.
What machines look like
A typical CNC foam cutter has two vertical towers, one at each end of a horizontal wire. Each tower can move the wire end up/down and front/back independently. By moving the two ends to different positions, the straight wire sweeps a ruled surface — that is how a wing that is fat at the root and thin at the tip gets cut in a single pass.
What can you actually make?
- RC and full-size model aircraft — wings, fuselages, tail surfaces (aerofoil sections).
- Architecture & signage — cornices, columns, 3D letters, logos, stage scenery.
- Industrial — packaging inserts, lost-foam casting patterns, insulation parts, ducting transitions.
- Hobby & art — cosplay armour blanks, sculpture cores, terrain for tabletop games.
Ready to try it? Jump to the Quick start, or read How hot-wire cutting works for the physics.