A standard yoga block is approximately 4 inches thick, 6 inches wide, and 9 inches long, or 10 by 15 by 23 centimeters. Special use blocks are made in other sizes.

Blocks come in a variety of materials. The most common, and perhaps least expensive, are made of a plastic foam. They come in a wide range of colors and are frequently included in “yoga starter kits”. These blocks are very light weight. Unfortunately, if you put weight on them they deform, giving you little support in a standing pose.
soft foam block

There is another variety of plastic foam that is more rigid and also comes in a variety of colors. These blocks keep their shape under pressure. While they don’t collapse they don’t provide as much feedback as wooden blocks.
solid foam block

More expensive, but still light-weight, are hollow wooden blocks. These are closed wooden boxes and can be made of bamboo or expensive hardwoods. These blocks don’t change shape under weight. Though very sturdy, over time the joints may loosen slightly.

Solid wooden blocks are generally made of pine, a lighter-weight, inexpensive wood. Solid blocks are sometimes made of hardwoods, which are heavier and more expensive than pine blocks. Solid blocks are very long-lasting though the extra weight causes problems for some people.
wood block

Another option is cork. This is the same material used for bottle stoppers and bulletin boards. Cork blocks weigh a bit less than some of the solid wooden blocks. While it doesn’t deform like the inexpensive foam blocks it can chip on the edges with use.
cork block