The BF Dry has a Fiberglass element that helps reduce the ingress of Water particulate into tanks and reservoirs. The BF 30 Oleophobic (SO902) is designed to coalesce oil mist in the breather and allow it to drip back into the tank or reservoir. The reduces the oil mist from escaping the tank through the breather and also reduces the builtup of dirt around the tank or reservoir filler.