A clean hot-wire finish comes from the wire melting, not tearing: aim for a taut wire, the lowest heat that still cuts at your feed, and a steady feedrate. Rough or fuzzy edges mean the wire is too cool or moving too fast and dragging; droopy melted edges mean too hot or too slow.
A smooth, slightly glazed surface is the target. Use fresh, straight wire (kinked or oxidised wire cuts unevenly), keep tension high, and avoid stopping mid-cut (the wire over-melts where it dwells). XPS finishes smoother than coarse-bead EPS, so material matters too. Once dialled in, a hot-wire cut often needs no sanding at all.
A smooth, slightly glazed surface is the target. Use fresh, straight wire (kinked or oxidised wire cuts unevenly), keep tension high, and avoid stopping mid-cut (the wire over-melts where it dwells). XPS finishes smoother than coarse-bead EPS, so material matters too. Once dialled in, a hot-wire cut often needs no sanding at all.