A water bottle cage is deceptively simple. It has one purpose - to hold your water bottles safely and assuredly on your bike. It's good to add both those words, since you don't your water bottles flying out of their cages when you're in a pack ride situation. That's the safety factor. Then there is the assuredly part, which means that you want your water bottles to be secure in their cages while you're riding, not rattling around and causing any distraction while you're riding. You need to reliably get your hydration and nutrition while riding, and the right bike cages are necessary to do so. Cages were made mostly out of aluminum until the carbon material explosion took off in the 90's. Now, there is a wide range of carbon water bottle cages out there. But want to know something about aluminum versus carbon water bottle cages? The carbon cages are a whole lot of hype. First of all, there is the cost factor. You can put a price per gram that you save on your bike, be it from the weight of the bike cranks, the stem, the pedals, etc. And there isn't a whole lot of weight savings in carbon bottle cages. A comparable cage in a given brand's lineup of cages might weigh 48g in the aluminum version for $8, then 34g in the carbon version for $45. Is it really worth a $30+ price difference for 14g of weight savings? That works out to $2 per gram. You can figure comparable numbers for cost savings for other bike parts and realize there is potentially a lot more bang for your buck saving weight in other areas as compared to water bottle cages. And second of all, carbon cages have a known history of sometimes self-destructing under duress. What comes to mind when saying this is many stories about carbon bottle cages cracking and falling apart, in essence, while bombing hills at high speeds. No one particular brand is thought of when saying this, but you could do, and should do, research on the reliability of a particular carbon water bottle cage before buying one. There are also titanium water bottle cages, by the way, which clock in at about the same weight as carbon ones. The most famous titanium water bottle cage out there is the King bottle cage, known for being a very high quality, long-lasting bottle cage. Long-lasting as in, for life. And with a weight in the sub 40g range, it's light. The only thing is, they come in natural titanium only, so you don't have color choices with them. All in all, you'll do just fine getting an aluminum bottle cage in the $2 to $10 range, knowing that each will weigh in at 40g to 60g. It should be mentioned, there are plastic composite material bottle cages such as theSpecialized cagesthat range from $10 to $20. There are also Profile water bottle cagesmade from advanced polymer plastic-like materials which have proven themselves very reliable, particularly for triathlon in the off-the-back bottle setups. These are sometimes listed as fiberglass water bottle cages. So there you have it - aluminum $2 to $10, plastic $10 to $20, carbon in the $20 to $50 range, and the rare titanium water bottle cages that run in the $50+ range.