I think most of you realize this, but all urethanes and resin balls are basically urethane. It is the resin additive, which I believe has varied substantially over the years in different balls. Early resin balls ( excalibers turbo x ) had a lot more additive that made them feel very sticky, sometimes to the point of being bleeders. Later generation resin balls never felt quite so sticky.
Also, I was just thinking, but the resin ball is now slightly over 20 years old. It was the last real breakthrough in shell technology. Urethane itself came out in 81, and the soft shelled polyester balls became popular in about 1973.
Soft polyester, urethane, and resin enhanced urethane were all revolutionary. Nothing to really compare to them in the last 20 years. Core technolgy has evolved, but nothing earth shattering.
The biggest change has really been in the volume and viscosity of oils being used. People wonder how we could get polyester and urethane to hit in the 70's and early 80's, but they don't understand we were playing on less than half the oil volume and the viscosities were about 1/3 of what they are today. Also during almost the entire urethane era oil was only buffed out to 24 feet.