PPI, etegeeza omuwendo gw’ebituli buli yinsi, ye yuniti y’okupima obungi bw’ebituli mu sipongi.PPI enkulu etegeeza nti obutuli mu sipongi bwa silikoni buba bunene.
Sipongi ya 40ppi silicone erina obunene bw’obuziba obunene (obunene bw’obuziba obutono), obutambuzibwa empewo obulungi (obunene bw’empewo obweyongera ebitundu 30% okutuuka ku 50%), era kyangu okuyonja. Kituukira ddala ku mbeera ezeetaaga okuyita kw’empewo okw’amaanyi oba okuyonja ennyo, gamba ng’enkola z’okusengejja empewo.
Sipongi ya 60PPI, olw’obutuli bwayo obw’amaanyi (nga 50% yeeyongera mu buziba), ekola nnyo mu nsonga z’okuziyiza amaloboozi (okukendeeza ku nnyiriri za 8-12dB) n’okuziyiza ebbugumu (okuziyiza ebbugumu kweyongera ebitundu 20%-35%), ekigifuula entuufu ey’okukozesa yinginiya w’amaloboozi oba okukozesa ebbugumu.