Dog food types
Why do some kibbles float and others sink in water?
Last updated 23 September 2026 · How we write and check this
Short answer
Floating comes down to density and trapped air from the extrusion process, not a marker of quality. Kibble expands as it exits the extruder, and pieces with more internal air pockets float, while denser, less expanded pieces sink, both of which can come from perfectly good formulas.
What determines density during extrusion
As dough exits the extruder under pressure, steam trapped inside expands the piece, similar to popcorn puffing. Formulas with higher starch content, or run through different die pressure settings, expand more and trap more air, making them float.
Why this is not a quality test
Some owners assume floating kibble means it is full of air and cheap filler, but expansion level is a manufacturing choice tied to texture and mouthfeel, not a reliable indicator of nutrient content or protein percentage.
What to check instead if you are worried
Rather than judging by the water test, check the guaranteed analysis on the bag for protein, fat, and fiber percentages, and look at whether a named meat is the first ingredient.
Key takeaways
- Floating or sinking in water reflects air trapped during extrusion, not nutritional quality.
- Denser pieces are not automatically better and airy pieces are not automatically worse.
- The guaranteed analysis panel is a more reliable way to judge a food than a home water test.