PPI a ɛkyerɛ ntokuru dodow a ɛwɔ nsateakwaa biara mu no yɛ ade a wɔde susuw ntokuru a ɛwɔ sponge mu no denden.PPI a ɛkorɔn kyerɛ sɛ ntini a ɛwɔ silicone sponge no mu no yɛ den.
40ppi silicone sponge no wɔ pore size a ɛsõ (ɛba fam pore density), mframa a ɛtumi fa mu yie (mframa dodoɔ a ɛkɔ soro 30% kɔsi 50%), na ɛnyɛ den sɛ wobɛhohoro mu. Ɛfata ma tebea horow a egye mframa a ɛkɔ soro anaasɛ ɛho tew mpɛn pii, te sɛ mframa a wɔde yiyi mu.
60ppi sponge no, esiane ne pores a ɛyɛ den (a ɛwɔ 50% nkɔanim wɔ pore density mu), yɛ adwuma kɛse wɔ nnyigyei a ɛmma nsu ntumi nkɔ mu (dede a ɛso tew 8-12dB) ne thermal insulation (thermal resistance kɔɔ soro 20%-35%), na ɛma ɛfata ma acoustic engineering anaa ɔhyew insulation applications.