Urethane has the lowest absorption rate of all three cover technologies. Traditional urethane reads the lanes very early with little overall and down lane motion. This is beneficial on lower volumes patterns and shorter pattern lengths to control the break point down lane.
Microcell Polymer is a new technology that absorbs oil, unlike traditional urethane, but at a fraction of the rate of reactive resin. This allows for more mid-lane read and greater continuation than urethane. This allows Microcell Polymer to provide a urethane-like reaction, but in today's modern environment of higher viscosity oils and more wet/dry conditions.
Reactive resin can absorb much more oil than both urethane and Microcell Polymer technology. Reactive resin covers allow for high hook potential and down lane motion.