Cello rosin falls into four main categories: light, dark, metallic and hypoallergenic. Typically, most cellists lean toward darker rosins because they provide better grip and a "larger" sound, but this depends on the venue. Metallic and hypoallergenic rosins are more expensive types but may be desirable based on the tone the player wants and how sensitive to irritants the musician is.
Similar to rosin for violins, violas and double basses, cello rosin most commonly is classified according to the color it has. The two broad categories are light and dark, but this is an extreme generalization, as a person can get rosin ranging from black to yellow-gold. In general, the lighter a rosin is, the harder and drier it is, and the less it grabs the strings. Violinists and violists thus lean toward lighter rosins because they don't need quite as much grip on their thinner strings. Cellists lean toward darker rosin by comparison, because their thicker strings require more grip that produces a bigger, grittier sound that carries better.
Even though a cellist should use a darker rosin in general, a player must consider his venue. Cellists sometimes prefer harder rosins for areas such as studios, because it provides a smoother sound that is better suited to the chamber setting. They move to a softer rosin for the concert hall where a fuller tone is required. Additionally, environment is a factor. Dark rosins, which are a little stickier, work better in a very dry climate, whereas light rosins, which are a little drier, are better where it's humid.
The type of strings on which a cellist plays also matter. Strings on a cello may be gut or wound, synthetic or steel. Each of these has different qualities that affects vibration and thus needs a different type of cello rosin. Steel strings work best with harder, drier rosins. Synthetic strings require a rosin of medium hardness and color, while gut or wound strings need a darker, stickier cello rosin.
Manufacturers also may classify cello rosin based on whether it has metallic additives. The metal in a rosin is thought to affect not only the grip provided, but also the tone the player can produce. These rosins tend to be much more expensive, particularly if they contain metals such as gold or silver. Some players assert that it is far better to get a good tone from proper technique and that it is a mistake to rely on more expensive metallic rosins for a particular sound.
Another broad class of cello rosin is hypoallergenic rosin. These are designed to produce less dust that can trigger a reaction in the musician. Hypoallergenic rosins, similar to metallic ones, tend to be pricier, although many cellists are willing to deal with the price increase for sneeze-and-irritation-free playing.