Insulated concrete panel billets

1. A cast concrete panel comprising:

a) a lower layer of concrete;

b) a plurality of spaced longitudinal prestressing cables through the length of said concrete panel;

c) foam billets above said lower layer of concrete positioned between said prestressing cables;

d) a plurality of staggered, spaced foam billet blocks positioned between said billets; and

e) an upper layer of concrete surrounding said billets and billet blocks and being bonded to said lower layer of concrete.

2. The cast concrete panel of claim 1 wherein said staggered, spaced foam billet blocks are further positioned adjacent longitudinal edges of said concrete panels.