It was an aggressive (for the day) pure urethane with a bulb shaped weightblock. Manufacturers were still experimenting with two piece technology, so the core dynamics aren't strong at all by todays standards.
Now, the purple one was called the Nitro purple haze and was not as aggressive as the dark blue one.
The other ones mentioned were all reactive resin. The Nitro/R was lime green with the same weightblock as the urethane models. The Nitro/R2 and pearl were light purple with an early version of the V2 core.
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