In yoga, the concept of ahimsa instructs us to “do no harm”—not to ourselves, not to others, and not to the planet. Last Wednesday, Lime.com reviewed several yoga mats that take kindness to our environment seriously, either through nontoxic manufacturing, sustainable and biodegradable materials, or both. Today, we look at the yoga mat's popular companion—the block, in search of the same eco-friendliness.

Blocks, and props in general, were an innovation of Iyengar yoga, but today are used more widely. Anyone whose palms strain to meet the floor in a forward fold or who seeks greater stability in balancing poses can reach for a block. In seated positions, a block under the tuchus adds height, encouraging the lower back to relax and the hips to open.

There are fewer planet-conscious yoga blocks available than mats, but here are two we like. Choosing between them entails assessing their “personalities” to complement your own, sort of like picking a mate.

If a strong, polished exterior, commitment to the environment, and the prospect of long-term commitment makes you swoon, the bamboo blocks from Barefoot Yoga Co. ($23, $42/pair) may be the block of your dreams. Bamboo's tensile strength is similar to steel, yet despite being so durable, it's amazingly light weight. Although this block is hollow, it feels solid, with no “give” in the joints. Since it's smooth and hard, you don't want to apply diagonal pressure (as in downward dog) unless it's placed on your mat or another non-slip surface; better to keep things perpendicular. If you're careless, you might accumulate scuff marks over time, but given its superior durability, it'll stick around despite your abuse. Plus, you will literally spare a tree by buying it, as bamboo isn't wood—it's a fast-growing, sustainable grass, harvestable within five years unlike decades for trees. Your pranayama might improve too, knowing that this tall tropical grass snatches more carbon dioxide from the air than trees, and in turn, releases more oxygen. As with many natural products, expect slight variations in color and grain pattern.

For a more accepting partner that gives a little under pressure (but has inner strength too), opt for the solid cork block from Hugger Mugger ($10.95-$13.95). Cork, a type of tree bark that is harvested annually by stripping it from trees, grows back fast enough to be sustainable. This natural-material block has a slightly heavier feel than conventional foam, and feels comforting in the hand. It has excellent traction on a hard floor, and a slight, unexpected springiness that inspires a confident grip, so you can focus the mind on something more important. How long this brick will last, given its composite construction, most likely depends on how clumsy you are. If you drop it frequently, the rounded edges and corners seem certain to dent. How heavy perspiration and the oil in your skin affects cork is unknown, but my guess is that the cork will naturally darken where you touch it most often. Lastly, you'll remember this prop's pleasant earthy smell, especially if you support your forehead with it in a seated forward fold. When was the last time you closed your eyes, breathed deeply, and imagined playing in the backyard?

Choosing between the two really comes down to taste. Do you want a hard, polished block that will last, or an earthy, non-skid block that might develop a patina of age, just like people do?

Of course, there's no need to settle down with just one. You could buy both—one for each hand.

Gaiam Cork Yoga block

Cost: $14-20

Where to Buy it: Gaiam

Bamboo block from Barefoot Yoga Co. super strong, bamboo will far outlast the common foam block

Cost: $23, or $42/pair

Where to Buy it: BarefootYoga.com and select yoga studios

Cork block from Hugger Mugger

Cost: $10.95-$13.95

Where to Buy it: Hugger Mugger or Amazon.com

Photo: HuggerMugger.com