Abstract: The invention concerns the transformation of expanded polymers, in particular styrene polymers of the polystyrene type and styrene copolymers. More particularly it concerns a method for transforming polymers in an expanded solid state into a non-expanded amorphous state in the form of a re-usable malleable pasty magma. The method comprises a step for treating the polymer with a transforming solution containing a solvent, a non-fatty lubricant and optionally an alcohol. The invention concerns the transformation method proper, the transforming solution used in said method, the device for implementing said method and the magma resulting from implementing the method.