Lub ntsiab tivthaiv ntawm cov yas yog cob. Lo lus "ream" yog lub npe hu ua tom qab lipids secreted los ntawm cov nroj tsuag thiab tsiaj, xws li rosin, shellac, thiab lwm yam. Resin hais txog lub khob tshuaj polymer uas tsis tau muab sib xyaw nrog ntau yam khoom siv. Lub reinc khwv yees li ntawm 40% mus rau 100% ntawm tag nrho qhov hnyav ntawm cov yas. Cov khoom ntawm cov yas yooj yim yog txiav txim siab los ntawm cov khoom ntawm lub pob, tab sis cov khoom siv kuj ua ib qho tseem ceeb. Qee cov khoom uas yeej muaj los ntawm cov khoom cua tawv, nrog los sis tsis muaj cov additives, xws li iav organic, polystyrene, thiab cov zoo li.
Lub npe hu ua yas, qhov tseeb, nws yog ib qho khoom siv hluavtaws, qhov zoo ntawm cov duab uas muaj lub pob zeb zoo li lub paj ntoo, zoo li cov tshuaj hu ua artificial synthesis, thiab hu ua yas.