I-PPI, ebhekisela kwinani lemingxuma nge-intshi nganye, iyunithi yokulinganisa ukuxinana kwemingxuma kwisipontshi.I-PPI ephezulu ithetha ukuba i-pores kwi-sponge ye-silicone iyancipha.
I-sponge ye-silicone ye-40ppi inobukhulu obukhulu be-pore (i-pore ephantsi ye-pore density), i-air permeability engcono (ukunyuka komthamo womoya nge-30% ukuya kwi-50%), kwaye kulula ukuyicoca. Ifanelekile kwiimeko ezifuna ukugqithiswa komoya ophezulu okanye ukucocwa rhoqo, njengeenkqubo zokucoca umoya.
I-sponge ye-60ppi, ngenxa yeepores zayo ezixineneyo (kunye nokwanda kwe-50% kwi-pore density), yenza ngokugqithiseleyo ngokwemiqathango yomsindo we-insulation (ukunciphisa ingxolo ye-8-12dB) kunye ne-thermal insulation (ukuchasana kwe-thermal kwanda ngama-20% -35%), okwenza kube yinto efanelekileyo yobunjineli be-acoustic okanye izicelo zokufudumeza ukushisa.