Solid plastic pieces
Two kinds of solid plastic pieces have been manufactured. Solid pieces are not stackable, but are slightly heavier than the modern hollow pieces.
The first, available in reasonable quantities, were resin pieces manufactured by Icehouse Games, Inc. These pieces are known for having brittle points and for sticking to each other.
Manufactured in much smaller quantity were the "unbreakable" pieces, molded from a high-impact plastic.