Ib qho tseem ceeb ntawm cov khoom ntawm plastics yog los ntawm kev ua tiav lossis kev tsis tiav ntawm lawv daim ntawv, lossis seb lawv yog: thermoplastics lossis thermosetting polymers. Thermoplastics yog cov khoom uas, thaum rhuab, tsis txhob siv cov tshuaj hloov hauv lawv cov muaj pes tsawg leeg thiab thiaj li tuaj yeem ua molded dua. Piv txwv li: polyethylene (PE), polypropylene (PP), polystyrene (PS) thiab polyvinyl chloride (PVC). Cov thermoplastics ntau ntawm 20,000 rau 500,000 amu, thaum thermosets yog assumed muaj infinite molecular luj.
Cov thermosets, lossis thermosetting polymers, tuaj yeem tsim thiab coj zoo ib zaug xwb: tom qab lawv tau ua tiav, lawv nyob ruaj khov. Hauv cov txheej txheem thermosetting, tshuaj lom neeg tshwm sim tuaj yeem ua tsis tau rov qab. Tus nplaum ntawm rubber yog ib qho piv txwv ntawm cov txheej txheem thermosetting: ua ntej cua sov nrog cov tshuaj sulfur, polyisoprene yog ib qho khoom siv, khoom nyuab me ntsis; tom qab vulcanization, qhov khoom yog tsis yeem thiab tsis-tacky.