Liquid Formulation of blowing agent

A formulation for foaming a thermoplastic polymer, for example PVC, comprises a carrier, a chemical blowing agent and 1 wt% or less, preferably less than 0.2 wt% of water. The liquid formulation can readily be used for foaming PVC and other thermoplastics. Preferably the blowing agent is either i) an exothermic blowing agent such as azodicarbonamide (ADC), oxybissulphonylhydrazine (OBSH) or a mixture thereof, ii) an endothermic blowing agent such as sodium bicarbonate, or iii) a mixture of exothermic and endothermic blowing agents.