Well, I thought someone would answer after the last hint.
FOAM is a dispersed GAS in a liquid and provides no lubricating qualities.
When engine components whip the oil in a crankcase the oil foams and bubbles form. Foam is simply entrained air.
When using a foam inhibitor such as polydimethylsiloxane (PDMS), the PDMS lowers the surface tension of bubbles and causes them to burst earlier than they would without PDMS in the oil.
PDMS is added to PCMO's at about 3-5 ppm treat levels and shows up as "silicone" in VOA's.
BTW, A foam inhibitor is actually a misnomer as it doesn't stop bubbles from being formed; it just causes them to burst sooner.