Sodium bentonite makes better clumping cat litter. It swells to many times its dry volume when wet and binds urine into firm clumps that lift out cleanly. Calcium bentonite absorbs liquid but swells far less, so its clumps are soft and break apart. Calcium bentonite can be treated with soda ash to behave more like sodium bentonite ("sodium-activated"), but natural sodium bentonite remains the benchmark for premium clumping litter.
Two litters can both say "100% bentonite" on the bag and perform very differently. The reason is usually the type of bentonite inside. Here is how to tell sodium from calcium, and why it matters for your shelf.
What bentonite is
Bentonite is a clay formed from weathered volcanic ash, made mostly of the mineral montmorillonite. Montmorillonite is built from thin layers with charged particles, called exchangeable ions, between them. When those ions are mainly sodium, the layers spread apart and soak up large amounts of water. When they are mainly calcium, the layers stay closer together and the clay swells much less. That single difference decides how well the litter clumps.
Sodium and calcium bentonite side by side
| Property | Sodium bentonite | Calcium bentonite |
|---|---|---|
| Swelling | High; expands to many times its dry volume | Low |
| Clumping | Firm, fast clumps that lift out whole | Soft clumps that can crumble; often sold as non-clumping |
| Odour control | Strong: urine is locked in clumps and removed | Absorbs, but liquid spreads further before it is held |
| Litter used per month | Lower, because only the clumps are scooped out | Higher, because the whole tray needs changing more often |
| Dust | Depends on screening and dust extraction | Depends on screening and dust extraction |
| Price per ton | Usually higher | Usually lower |
| Typical use | Premium clumping litter | Economy and non-clumping litter, or blends |
What "activated" bentonite means
Calcium bentonite can be mixed with soda ash (sodium carbonate) so that sodium takes the place of some of the calcium between the clay layers. This "sodium-activated" bentonite swells more than untreated calcium bentonite and clumps better. How well it works depends on the clay and on how carefully it is treated, so results vary from one producer to the next. If a supplier offers activated bentonite, ask for the swell index and test a sample next to a natural sodium bentonite.
How to tell what you are buying
- Ask the supplier directly whether the clay is natural sodium, natural calcium or sodium-activated calcium bentonite.
- Check the swell index and montmorillonite content on the data sheet. Sodium bentonite scores much higher on swelling. Our guide to reading a cat litter spec sheet explains both.
- Run a pour test. Pour a little water onto a sample. Sodium bentonite forms a firm clump within moments that holds together when lifted; calcium bentonite stays soft or falls apart.
- Compare samples with bulk. Repeat the pour test on the first shipment.
Which should you buy?
For a clumping litter sold to cat owners in pet shops, supermarkets and online, choose sodium bentonite: shoppers judge litter by how well it clumps and how long a bag lasts. Calcium bentonite can make sense for a low-price, non-clumping line, or as part of a blend where cost matters more than clump strength. If you are building a private-label brand, start from sodium bentonite and adjust granule size and fragrance to suit your market.
What FELUXE uses
Every FELUXE formula is made from natural sodium bentonite mined by our own group in Semnan province, Iran. It has a montmorillonite content of 80, a swell index of 20 and an absorption capacity of up to 800%. We make it in three formulas, Standard, Activated Charcoal and Lavender, available under your own brand or in 1-ton bulk bags. For more on why bentonite leads the market, read why bentonite is the gold standard for cat litter.
Frequently asked questions
Is sodium or calcium bentonite better for cat litter?
Sodium bentonite is better for clumping cat litter. It swells far more than calcium bentonite, so it forms firm clumps that lift out whole and lock in odour. Calcium bentonite suits cheaper non-clumping litter.
What is sodium-activated bentonite?
It is calcium bentonite treated with soda ash (sodium carbonate) so that sodium replaces some of the calcium in the clay. It swells and clumps better than untreated calcium bentonite, but results vary by producer, so check the swell index and test a sample.
Is FELUXE sodium or calcium bentonite?
FELUXE is natural sodium bentonite, mined by our own group in Semnan province, Iran, with a montmorillonite content of 80 and absorption of up to 800%.