A blowing agent blend for making thermoplastic polymer foams comprises
methyl formate. The blowing agent blend can further comprise at least one
co-blowing agent. The co-blowing agent is either a physical co-blowing
agent (e.g. an inorganic agent, a hydrocarbon, a halogenated hydrocarbon,
a hydrocarbon with polar, functional group(s), water or any combination
thereof), or a chemical co-blowing agent, or combinations thereof. The
thermoplastic polymer foam can be an alkenyl aromatic polymer foam, e.g.
a polystyrene foam. The blowing agent blend can comprise any combination
of methyl formate and one or more co-blowing agents. The methyl
formate-based blowing agent blends produce stable foams for various
applications, including containers, packaging systems, as well as
insulation boards and building materials. A process for the preparation
of such foams is also provided.