Vinamold is one brand name (Gelflex is another) for a meltable vinyl compound used for mouldmaking which turns liquid at around 140 C. It has a similar flexibility to silicone and is re-usable, though detail reproduction is not as good.
Comes as a solid slab which can be sliced into pieces for heating in either specially designed ‘kettle’ or with care in a saucepan on low, controllable heat. Melts reasonably quickly. Both brands (Vinamold and Gelflex) have ‘hard’ and ‘soft’ varieties. Moulds accept all casting materials, including silicone. Repeatedly re-meltable especially if cared for i.e. not allowed to overcook and stored wrapped or contained. Unreliable detail reproduction (due to immediate cooling on contact with prototype), prototypes must resist heat, not versatile (only 2 types, only for block pouring), limited durability and mould-life. Mixing/working guide: not mixed with anything just melted, ready as soon as cool. Average cost: £8 per kg