Foam, plastic, metal and wood can all be used to make the masters of anything needed to be moulded. Often if the design is of a facade or has intricate details then they can be laser cut and then silicone moulds are normally made from those. This means that any sections can then be cast in materials such as resin, foam, fibreglass or plaster. Fibreglass is a good material to use as it can produce sturdy but lightweight shells. If however the miniature needs to be blown up a material has to be used that when exploded will produce small enough break away sections for that scale of model. Normally the material that most effectively produces this effect is specially mixed plaster.
Destructive Plaster: This is plaster mixed with baking soda, sawdust or any other material that will keep the plaster light and make it crumbly when set.