During a transition, yes — that is how a transition works. Permanently, it makes clumping unpredictable, and unpredictable clumping is what jams automatic boxes.
Mixing is a method, not a state.
During a switch
A quarter new for a few days, then half, then most. Cats object to sudden substrate changes more than to the substrate itself.
Permanently
Different granule sizes and setting speeds produce clumps that hold together inconsistently. A rake or a drum needs a clump it can lift intact, and mixed litter is where that becomes a coin toss.
Never mix these
Crystals with clumping clay. Two incompatible mechanisms in one tray, in a machine designed for one of them.
The exception
Some manufacturers sell mixed litters — tofu with corn or apple wood pellets, for instance — formulated to clump as one material. That is a product, not a mix you make.
Last reviewed 2026-08-17