Ib lub pwm uas siv cov ntawv yas thiab cov ntawv ua cov ntaub ntawv raw los tsim qee cov khoom yas yooj yim. Nyob rau hauv cov ntaub ntawv ntawm softening, nws yog deformed thiab txuas mus rau lub kab noj hniav ntawm cov pwm kom tau cov khoom pwm xav tau, uas yog tsuas yog siv nyob rau hauv zus tau tej cov khoom siv niaj hnub, khoom noj khoom haus thiab cov khoom ua si ntim khoom.
Vim tias qhov tsis tshua muaj siab thaum lub sijhawm molding, cov khoom siv pwm feem ntau yog ua los ntawm cam khwb cia txhuas lossis cov khoom tsis yog xim hlau, thiab cov qauv kuj yooj yim.