This study is concerned with the "up-cycling" postconsumer wastes into the value-added products of multiwall carbon nanotubes (CNTs). It investigated combinations of methods for pretreating different types of stainless-steel catalysts that increase the yield of CNTs form common waste plastics. The polymers were pyrolyzed at 800 degrees C, in nitrogen, and their gaseous pyrolyzates were passed over fixed catalyst substrates preheated to 800 degrees C. The substrates consisted of SS-304, SS-316 and SS-316L fine stainless-steel wire-cloths. Therein synthesis of CNTs took place by chemical vapor deposition (CVD). The wire-cloths were used either as-received or chemically etched by acid wash and/or heat-treated in air, nitrogen or helium at 800 degrees C, and then rapidly air-quenched. Results showed that the catalyst type, composition and pretreatment method, as well as the type of feedstock, are all influential on the yields and physical characteristics of the synthesized CNTs.