In general, cat experts are not fond of crystal cat litter, which is made out of dried silica gel. However, this type of kitty litter is popular with some cat owners for a very understandable reason: a single usage of crystal litter can last in a cat litter box for an entire month, thanks to the super-absorbency of sodium silicate, the same material that's packed into pill bottles to keep their contents dry. (Of course, this only applies to cat urine; you still have to scoop out your cat's solid waste every day.) Because they don't have to be changed as often as clay or biodegradable litters, crystal cat litters come in more manageable bag sizes (as small as 4 pounds), a big plus for cat owners who are unable to do heavy lifting.
However, as convenient as crystal litters can be for people, cats are likely to see things from a different perspective. The tiny, jagged crystalline particles can be very hard on a cat's sensitive paws. Even if your cat consents to using a crystal litter, it may not be very happy about it. There's also a downside from the human perspective: once a portion of crystal litter has reached its absorbency limit, you'll end up with a pool of urine in the bottom of the cat litter box.
As with fine-grained clumping clay litters, because they're all made from pretty much the same ingredients, there's not much difference among individual brands of crystal cat litter. While not many brands of crystal litters receive consistently favorable feedback, Fresh Step Crystals (Est. $20 for 8 lbs.) stands out among user review sites. It generates more than 1,000 reviews at Walmart.com, earning 4.5 stars out of 5, with 96 percent of owners saying they'd recommend the cat litter to a friend. Judging from reviews, it's one of the better choices out there, though it has the same pros and cons you'd expect from a crystal cat litter. It's extremely absorbent, doesn't need to be changed frequently and is economical. Still, it's not biodegradable, and as mentioned above, the silica gel crystals may be hard on a cat's feet.
You should bear in mind that some manufacturers (such as the makers of Scoop Away, Tidy Cats and Ever Clean) offer clumping clay/crystal blends that combine the clumping action of fine-grained clay with the super-absorbency of crystals. Although we haven't specifically covered any of these products because there aren't a significant number of reviews, if you're searching for the perfect cat litter it may be worth buying a small bag of one to see how well it works.