Magnesium carbonate (MgCO3) has long been used by gymnasts to improve their grip on bars, rings or vaulting horses. Climbers, too, use chalk for keeping hands dry and holds secure when climbing indoors and out.
A variety of chalk, bags and accessories are available to climbers. What you select will depend on your climbing style and the environment.
For shopping help, read on:
Block, Bulk or Ball?
Block chalk, or compressed magnesium carbonate, is standard gym chalk. It is the least expensive variety and can be used in a wide range of situations, providing friction and moisture absorption for the hands.
Loose bulk chalk is the workhorse for long outdoor routes. Fill up a large bag with the stuff and you'll be able to chalk up repeatedly all day. Some types of loose chalk are available with an added drying agent to absorb moisture for better gripping ability.
Chalk balls are sacks made of porous fabric filled with loose chalk. The sack keeps chalk dust contained in the bag as you apply it to your hands and prevents you from spilling it and breathing it. Chalk balls are the cleanest and healthiest choice for climbing on indoor walls. Chalk balls also last longer than loose chalk.
Chalk is typically white, but some varieties are available in colors to match the rock, leaving less of a visual impact. Some other types of so-called "chalk" are actually drying agents without color. They leave no trace on the rock.
Chalk bags come in a variety of sizes. Smaller bags are appropriate for indoor climbing, bouldering sessions and people with smaller hands. Larger bags are good choices for long routes or climbers with large hands.
Bags typically come in 2 shapes. Cylindrical bags typically hold more chalk and are good for finger dipping on longer climbs, while the tapered bags are suited for shorter sport routes.
Stiffened rim: Holds the bag open for easy dipping.
Fleece lining: Holds down the chalk dust and distributes the chalk evenly on your hands.
Cord and toggle closure: Keeps chalk from spilling when not in use.
Chalk bag belt: Useful for when you're not wearing a harness, as in bouldering.
Toothbrush loop: Carries a toothbrush to clean old chalk off holds.