Hot wire tables (e.g. Proxxon THERMOCUT 115/E) are awesome. A snap-off utility knife will help you to get started but the hot wire table is worth it if you work a lot with XPS and the like. Makes precise cuts and is a pleasure to work with. Costs like $100 and takes quite a bit of space though.
A compass saw can come in handy when working with high density foam, but hot wire cutters are better. Saw stuff outside and wear a mask, the dust is messy and toxic.
Get a snap-off utility knife. A good general workhorse and the longer blade option definitely has its uses.
Optionally get a scalpel handle and blades for it. Hobby knives are inferior for most uses except removing mold lines. Get a good brand handle and blades from the same brand. Swann Morton is a good brand, 10A is a good blade size. Avoid knives with round handles as they might roll off the table.
Get a metallic safety ruler. Avoid cutting you own fingers. 15 - 30 cm is optimal; better if has both metric and inch measurements.
Hot wire pencils can be useful for sculpting high density foam e.g. Peter Child Artist's Pyrography machine. Soldering iron for electronics can work as a replacement.
Ventilation is always to be assumed when cutting with a hot wire. Most of the materials cut with a hot wire can release toxic fumes, don't inhale that stuff.
EPS and XPS foam cutting produces mostly just hydrocarbons and water vapor, so it is known to be relatively safe if you don't burn the material.
What you can cut with a hot wire cutter:
- EPS (Expanded Polystyrene) foam; the airy white foam used in packaging
- XPS (Extruded Polystyrene) foam; the dense smooth foam used for house insulation
- PE (Polyethylene) foam; the rough foam used for pool noodles.
- EVA (Ethylene-Vinyl Acetate) foam; the flexible material used in exercise and toddler mats. Cutting EVA might require high temperature depending on the type of EVA.
- EPP (Expanded Polypropylene); a foam used to package sensitive instruments.
You cannot cut PU (Polyurethane) foam with a hot wire, the material used in bed and sofa stuffings. Releases very toxic fumes and leaves a mess on the wire.
- Battlefields in Minature, Paul Davies
- Hot Wire Foam Factory - FAQ