Description: 521 synthetic resins or natural rubbers -- part of the class 520 series / 521 synthetic resins or natural rubbers -- part of the class 520 series/() synthetic resins (class 520, subclass 1) (50) cellular products or processes of preparing a cellular product, e.g., foams, pores, channels, etc. (79) extruding a solid polymer containing material to form a cellular product (81) system contains a mixture of solid polymer or at least one solid polymer and at least one solid polymer-forming system
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