1. What density counts as high density? What is the difference between density and firmness (ILD/IFD), and how do I choose?
Density determines durability and resistance to sagging (the higher, the more durable).
ILD/IFD determines the soft or firm feel and is independent of density, so a high density foam can also be made soft.
Sofa seat cushions commonly use 30-45 kg/m3 with a medium to high ILD; mattress support layers use higher density; comfort layers can use a lower ILD. Buyers usually ask for both parameters to be specified clearly.
2. Will it sag quickly? What is the service life?
Low density foam, or foam with an inflated density claim, deforms permanently within six months to two years. This high density, high resilience grade can last 5-10 years or even longer.
3. What is the difference between mattress and sofa use, and how should density be matched for different parts?
Sofa: seat cushions use high density and high resilience (to resist prolonged sitting), while backrests and armrests can use slightly lower density and be softer.
Mattress: the support layer uses high density and is firmer, while the comfort layer can use medium to high density with slow rebound.