A solid state foaming process permits the use of up to 100% recycled pre- and post-consumer polymer for the manufacture of foamed polymer material and thermoformed foamed polymer articles. The process enables the optional formation of integral unfoamed skins of controllable depth and crystallinity on foamed polymeric materails suitable for a wide variety of applications. Because this process does not alter the underlying chemistry of the material all scrap from the manufacturing process may be reused without additive to form new foamed polymeric materials and articles.