NOTE: These cacti came to us in a batch of unlabeled, unnamed, assorted cactus. We're not entirely sure what they actually are, so we're just naming them ourselves.
There's a pretty good chance that this cactus is an "Old Man Hair" or "Old Lady Hair" cactus (Mammillaria Hahniana) whose hairy outer layer helps protect the cactus, and stay cool in the hot deserts they call home. It just looks like the top of a giant Q-tip to us, so that's where our version of its name comes from.
Water: Give a shot glass worth of water once a week. Water less in winter. Avoid overwatering.
Light: Lots of bright, indirect sunlight.
Soil: Well draining mix is best. You can use a prepackaged cactus mix, or 3 parts sand, 1 part perlite, 3 parts potting soil.
Humidity: Cacti do not appreciate excess humidity or moisture. Keep in a drier area.
Fertilizer: Fertilize with a balanced cactus/houseplant fertilizer once a month during growing season.