Concentration of PDMS, hydrophobic agent choices, chemical hardeners in the compound, actual concentration of siloxane agents and silane agents for gloss and hydrophobics, then the actual bonding agent because there are no SiO2 agents that naturally bond to clearcoat. Bonding agent/solvent choices are the expensive parts of a SiO2 product, they're what dictates how much actual protection is left and how chemically dense the actual layer is. As well, it's also going to be how thick the actual layer is. I'm guessing PBL is probably sitting at 1 micron or sub 1 micron level, while Wolfgang may not form a thick enough layer to be detectable with your average paint thickness reader.