I-PPI, ebhekisela enanini lezimbobo iyintshi ngayinye, iyunithi yokulinganisa ukuminyana kwezimbobo kusipontshi.I-PPI ephakeme isho ukuthi izimbotshana zesipontshi se-silicone ziminyene.
Isipontshi se-silicone esingu-40ppi sinosayizi wembotshana okhudlwana (ukuminyana kwembotshana ephansi), ukungeneka komoya okungcono (ukwanda kwevolumu yomoya ngo-30% ukuya ku-50%), futhi kulula ukuyihlanza. Ilungele izimo ezidinga ukungena komoya okuphezulu noma ukuhlanzwa njalo, njengezinhlelo zokuhlunga komoya.
Isiponji esingu-60ppi, ngenxa yezimbotshana zaso eziminyene (enokwanda okungama-50% kobuningi bembotshana), senza ngokugqama kakhulu mayelana nokufakwa komsindo (ukunciphisa umsindo we-8-12dB) kanye nokufakwa kwe-thermal (ukumelana nokushisa kukhuphuke ngo-20% -35%), okwenza kube ngokufanele ubunjiniyela be-acoustic noma izinhlelo zokusebenza zokushisa ukushisa.