The process of extrusion occurs when a liquefied or molten material is pressurized and squeezed out through a shaped orifice or “dye”. Solidification occurs as rapid cooling and depressurisation occur as the material exits the dye. The material being processed may be plastic, metal or even a foodstuff.  The process is not especially polluting but there may be oil aerosols released if the dye is oil lubricated and/or there may be dust and moisture released especially in foodstuff extrusions. The point of extrusion may need to be enclosed but often thermal lift will cause any released fume or dust to rise making a close canopy an acceptable option. The filter type must cope with the contaminants that exist. For food, a stainless steel RotoClone W would usually be the first choice.