KTM Industries, a four-year-old firm in East Lansing, Mich., has developed a proprietary way to extrude flexible starch foam. Reactive extrusion of starch foam into sheet using water as the plasticizer and blowing agent is common in making snack foods, but the resulting foam is typically stiff and brittle, adding crispness. But brittleness isn’t desirable in packaging. KTM’s proprietary formulation adds mineral nucleating agents and biodegradable modifiers to create a flexible foam with a controlled closed cell structure. The foam is extruded into sheet 2 ft wide and 0.25 to 0.5 in. thick with a corotating twin-screw extruder from Wenger Manufacturing, Sabetha, Kan., a machine normally used in the food industry, not plastics. The flexible foam is used for packaging—e.g., laminated to paperboard. Presented in a paper at the SPE GEPEC conference in Atlanta in April, the foam was developed in cooperation with Michigan State University also in East Lansing.