Polystyrene Welding Rods.
These Trade flame Plastic Welding Rods are designed to be used with the Trade flame Plastic Welding Kit (part 213045).

is ideal for use on CD cases, plastic cutlery, imitation glassware, low cost brittle toys, foamed polystyrene cups and takeaway clamshells, protective packaging and building and food insulation and where welding of PS plastic is needed.