The invention relates to an extrusion agent comprising: at least one heterogeneous PVDF (A), in other words a copolymer of VDF and at least one comonomer of VDF, comprising by weight at least 50%, advantageously at least 75%, of VDF which has a melting point Tm (expressed in ° C.)>172-549 m, preferably >1.1×(172-549 m), where m denotes the overall molar percentage of comonomer(s); and at least one interface agent (B), which are optionally diluted in a polyolefin (C). The heterogeneous PVDF preferably has a Tm of between 160 and 172° C. Advantageously it is also a VDF-HFP copolymer containing, by weight, from 88% to 92% of VDF and from 8% to 12% of HFP. The extrusion agent is used to reduce or eliminate the surface defects which arise during the extrusion of a thermoplastic resin (D). This resin may be a polyolefin, a styrenic resin, a polyester or a PVC. Optionally it may also be filled, i.e., may contain dispersed organic or inorganic particles.