Plythyln r plythn (bbrvtd P; PC nm plythn r ply(mthyln)) s th mst cmmnly prdcd plstc. t s plymr, prmrly sd fr pckgng (plstc bgs, plstc flms, gmmbrns nd cntnrs ncldng bttls, cps, jrs, tc.). s f 2017, vr 100 mlln tnns f plythyln rsns r bng prdcd nnlly, ccntng fr 34% f th ttl plstcs mrkt.
Mny knds f plythyln r knwn, wth mst hvng th chmcl frml (C2H4)n. P s slly mxtr f smlr plymrs f thyln, wth vrs vls f n. t cn b lw-dnsty r hgh-dnsty nd mny vrtns thrf. ts prprts cn b mdfd frthr by crsslnkng r cplymrztn. ll frms r nntxc s wll s chmclly rslnt, cntrbtng t plythyln's pplrty s mlt-s plstc. Hwvr, plythyln's chmcl rslnc ls mks t lng-lvd nd dcmpstn-rsstnt plltnt whn dspsd f mprprly. Bng hydrcrbn, plythyln s clrlss t pq (wtht mprts r clrnts) nd cmbstbl.