Typically white foam made from beads - used for packing - density 15 to 45Kg/cu m - thermal conductivity 33mW/mK (for typical 20Kg/cu m foam). Can be cut with a Hot Wire Cutter.

There are two types of Expanded Polystyrene - Open Cell and Closed Cell. Open cell is where there are gaps between the beads, and closed cell where there are not. Open cell is not waterproof and closed cell is (as in polystyrene cups).

Extruded polystyrene is a thermal insulation material used in building construction. There are a couple of brands: Styrofoam by Dow and Polyfoam by Kanuf. Styrofoam (density 32Kg/cu m - thermal conductivity 27mW/mK) is light blue or pink in colour, while Polyfoam (density 38kg/m3 - thermal conductivity 35 mW/mK) tends to be orange or beige.

Extruded polystyrene has a foam texture, moisture resistant, significantly more rigid than Expanded Polystyrene and can be machined (with care). Can be cut with a Hot Wire Cutter.

Tips for working with Styrofoam:

Cutting: STYROFOAM™ brand foam cuts easily with a serrated knife, hacksaw, etc. Wax the knife blade with an old candle for easier, smoother cuts

Painting: Paint with an acrylic craft paint. Solvent-based paints may damage the foam

Gluing: For a fast, sure bond, use a low-temperature glue gun. Hot glue guns can be used but the hot glue may melt a small portion of the foam

Sanding: For smooth, rounded edges, “sand” the foam with another piece of STYROFOAM Brand Foam

Polystyrene foam tends to be difficult to glue - because the solvents in some glues attack it. Here are 3 glues that work well and don't attack polystyrene.

PVA wood glue - this works but you have to allow a long time for it to dry - especially on thick sections. Allow at least a day when working with sections of 1“ or more.

Epoxy resins - these set normally - between a few minutes to a day depending on type.

Silicone Rubber - as used for sealing plumbing & worktops - allow 24 hours to set.

Hot Glue Gun - set quickly and are relatively easy to apply.

Indicative strength (natural colour):

Braided cord works better than twine as twine tends to twist/untwist during the flight - causing the payload to spin.