Most comparisons of this kind list materials and their properties and leave you no better informed. The real difference is narrower and more specific than that, and it only shows up after a few months of use.
The actual issue is scratches
Plastic is soft. A cat's tongue is rough, its claws catch the rim, and the bowl gets moved, dropped and scrubbed. Within months the surface carries a network of fine scratches you can feel but barely see.
Those scratches hold onto food residue and moisture, and that is where bacteria and biofilm establish themselves. Washing removes what sits on the surface. It does not reliably reach into the grooves.
The most visible consequence in cats is feline chin acne: blackheads and small bumps along the chin and lower lip, from resting the chin on a contaminated rim at every meal. It is common, it is often mild, and switching bowl material is one of the first things vets suggest.
Odour and taste
Plastic is porous enough to hold smells, and it can impart a faint taste to water. You will not notice. A cat with a sense of smell roughly fourteen times sharper than yours may well, and a cat that finds its water faintly wrong simply drinks less.
What stainless steel does better
- It does not scratch the same way. Fewer grooves, less biofilm.
- Non-porous. Holds no odour or taste.
- Dishwasher-safe at temperatures that actually sanitise.
- Lasts. A steel bowl outlives several plastic ones, which closes most of the price gap.
The one real drawback: steel is light and slides, and some cats dislike the noise of a tag or claw against it. A weighted base or a silicone ring solves both.
Where ceramic sits
Glazed ceramic is as good as steel on hygiene, heavier so it stays put, and quieter. It is also breakable, and there is one genuine caveat: buy from a source that states the glaze is lead-free and food-safe. Cheap decorative ceramic is not always either.
For most households ceramic is the nicest option and steel is the most practical. Both beat plastic.
The comparison in one table
| Plastic | Stainless steel | Ceramic | |
|---|---|---|---|
| Scratch resistance | Poor | Good | Good |
| Holds odour | Yes | No | No |
| Linked to chin acne | Yes | No | No |
| Stays put | Poor | Poor unless weighted | Good |
| Breakable | No | No | Yes |
Shape still matters more
Worth saying plainly: a wide, shallow plastic bowl will serve your cat better than a deep, narrow steel one. Material affects hygiene over months. Shape affects whether your cat is comfortable at every single meal.
Get the shape right first, then the material.
General guidance, not veterinary advice. Persistent bumps or sores on the chin should be looked at by a vet rather than treated as a bowl problem.