Not all foam is hot-wire friendly. The two big rules: it must be a thermoplastic (melts when heated rather than charring), and it should not release nasty fumes. Polystyrene foams are the classic choice; a few others work with care; some must be avoided entirely.
The good ones
EPS — Expanded Polystyrene
The white "bead board" foam (coffee cups, packaging, builder's foam). Cheap, light, widely available, and cuts beautifully. Low-density EPS cuts fast and clean; cheap recycled EPS can have inconsistent bead size that causes tear-out. The workhorse of hot-wire cutting. Melts around 240 °C, softens much lower.
XPS — Extruded Polystyrene
The coloured insulation board (pink, blue, green — Styrofoam™ is one brand). Denser and finer than EPS, so it cuts to a smoother, harder finish that takes paint and sanding well. Slightly more heat / slower feed than EPS. Excellent for detailed parts and architectural work.
EPP — Expanded Polypropylene
Tough, springy, "bouncy" foam used for durable RC models. It can be hot-wired but is fussier: it wants a hotter wire and tends to leave a slightly rougher, stringier cut than polystyrene. Great when you need parts that survive crashes.
Cut with care
- PE (Polyethylene) — closed-cell packing/craft foam. Cuts, but melts gummy and can string; keep ventilation good.
- EVA — the foam-mat / cosplay foam. Hot-wire works for rough shaping but it melts and smells; many people prefer blades for EVA. Ventilate well.
- Floral / craft foam — varies wildly; test a scrap first.
Do NOT hot-wire cut
Quick comparison
| Foam | Cuts? | Finish | Notes |
|---|---|---|---|
| EPS | Excellent | Smooth, slightly beady | Cheapest, most common |
| XPS | Excellent | Very smooth, hard skin | Best for detail/paint |
| EPP | Good | Rougher, stringy | Tough, crash-resistant |
| PE | OK | Gummy | Ventilate |
| EVA | OK | Melty, smells | Blades often better |
| PU | No | — | Toxic fumes — avoid |
| PVC | No | — | Toxic fumes — avoid |
Density matters
Within a foam type, denser foam needs more heat or a slower feed than light foam, and gives a harder, more detailed finish. If your cuts are tearing, the foam may be too low-density or have uneven beads; if the wire bows, the foam is too dense for your current feed/temperature. The simulator's material info card lists melt/burn temps and a recommended feed for each foam.