Chalkbags, whether for bouldering or sport climbing, are a climbers best friend. Every climber has encountered the problem of moist and sweaty hands causing him/her to slip of a hold. That is why climbers fill up their bags with magnesium carbonate, aka chalk, to be able to quickly dry off that layer of moisture and assure safe grip on the next few moves. The difference between a climbers chalkbag and a boulderer's chalkbag is that the climber fixes his/her chalkbag around the waist in order to be able to chalk all the way along the route. A boulderer on the other hand does not need to carry the chalk bag into the problem, since they are generally climbing very short intense problems, and have a bigger chalkbag that can just stand on the ground by itself.
A climbers chalkbag should be light, small and handy to use. Easy and quick access is a must, hence the opening needs to be wide enough and is often reinforced to facilitate chalking. Furthermore, which is also necessary for a boulder chalkbag, the outside material of chalkbags should be water repellent and the closure system water proof, because the worst thing that can happen is for moisture to get into your chalkbag, it ruins your chalk and the whole purpose of drying your hands is lost.
Finally, the design of both boulder an climber chalkbags offers a huge variety of choice. Most chaklbags come with brush holders, some come with a zipper to hold on to valuables or whatnots. The final choice one has to make when purchasing a chalkbag is a personal one, there are so many prints, patterns and colours available that the choice seems endless.