Qhov ceev ntawm lub txaj ua npuas ncauj yog hais txog qhov hnyav ntawm cov npuas dej hauv ib chav tsev, feem ntau qhia hauv kilograms ib cubic meter (kg / m³). Qhov ceev dua txhais tau hais tias cov khoom siv ua npuas ncauj ntau dua, ua rau muaj kev txhawb zog thiab muaj zog dua. Qhov ntom ntom tsis tsuas yog cuam tshuam rau lub txaj firmness, tab sis kuj ncaj qha cuam tshuam rau cov npuas dej resilience thiab lifespan, ua rau nws yog ib qho tseem ceeb rau xaiv ib lub txaj txaj.
Tsawg- ua npuas ncauj ntom ntom (feem ntau 20-30 kg / m³) yog mos thiab xis, tab sis muaj qhov hnyav dua -cov kabmob muaj peev xwm thiab nws yooj yim rau sagging lub sijhawm. Nruab nrab- ua npuas ncauj ntom ntom (30-50 kg/m³) sib npaug softness thiab kev txhawb nqa, haum rau feem ntau tsev neeg. High-density ua npuas ncauj (tshaj 50 kg / m³) muaj kev txhawb zog thiab kev ua haujlwm siab, haum rau cov neeg hnyav dua lossis cov txaj txaj uas npaj rau kev siv mus sij hawm ntev, thiab tseem muaj lub neej ntev dua.
Thaum xaiv ib lub txaj txaj, qhov tsim nyog yuav tsum tau xaiv raws li qhov hnyav ntawm tus kheej, pw tsaug zog, thiab kev nplij siab xav tau. Cov tib neeg sib zog tuaj yeem xaiv qhov ua npuas ncauj qis rau nruab nrab kom muaj qhov muag muag thiab xis nyob; heavier individuals or those seeking long-term durability are advised to choose medium to high density foam to ensure the mattress does not sag and to support the spine and joints, maintaining a good sleeping posture.