Amorphous polyester foam

A method of expanding an amorphous polyethylene terephthalate polymer by use of a blowing agent mixture comprising a low permeability blowing agent and a high solubility blowing agent, wherein said method comprises:

• adding an effective amount of said blowing agent to said polymer;
• accumulating the resulting homogenous mixture of polymer and blowing agent in an accumulating chamber;
• pressurizing said accumulating chamber and ejecting the polymer-blowing agent melt under such pressure through a die orifice to extrude and expand said polymer-blowing agent mixture.

A method of expanding a resin particle comprising an amorphous polyethylene terephthalate polymer and a blowing agent mixture, said blowing agent mixture comprising a low permeability blowing agent and a high solubility blowing agent, said method comprising:

• heating said resin particle at a temperature of from about 90.degree. C. to about 160.degree. C. for a sufficient period of time to allow for expansion to occur.

A method of forming a low density foam from an amorphous polymer comprising:

• adding a blowing agent to an amorphous polyethylene terephthalate polymer;
• and
• expanding said foam to a density of 15 pcf or less.

A low density foam having a density less than about 15 pcf, said foam comprising an amorphous copolyester resin and a blowing agent, said copolyester resin formed from polyethylene terephthalate and a reaction product of a cyclic alkyl diol and terephthalic acid.