Gaiam yoga block is essential for yoga beginners. Unless your naturally very flexible, then you will need this product. This is helpful when you need to keep your legs straight and your hands have to be on the floor. If they can't reach the floor then you use the yoga block. I use the block in the highest dimenstion (verticle) because I really can't touch the floor. When we're in half-moon pose with one arm towards the ceiling, and one hand on the ground, I place this block horizontally.
It is a thick foam block that doesn't place unwanted pressure on the wrist. I believe it can support just about any human weight. this block is also very light and easy to transport. This block has a nice surface and is very difficult to slip from. I wish that i had bought the bigger one, because sometimes it seems that I would need two to support my balance.
This product came with a yoga DVD that I haven't looked through yet, but it's a great deal from Target.