Why Doesn’t Plastic Totally Dry in the Dishwasher?

There are certain household questions that are constantly asked, yet almost never answered: “Where does the other sock go?” “Who keeps putting the nearly empty water pitcher back in the fridge?” “Why does everything in the dishwasher come out dry except the plastic?”

The last one, at least, has an answer. It comes down to how the material holds heat, and how water behaves once it lands on it.

Plastic Doesn’t Hang on to Heat

The first thing to know is that dishwashers use heat from the final, hot water rinse to dry dishes. This water makes the dishes hot, and the water clinging to them evaporates as they cool. The longer a dish stays hot, the drier it gets. Some midrange to high-end dishwashers have additional heating mechanisms that can be flipped on to help speed up drying, but even then, some of your plastics will likely come out damp. And it’s all because of how plastic holds heat.

Plastic can hold more heat than glass or ceramic ounce for ounce. But plastic containers are thin and light, while a ceramic plate is dense and heavy. More mass means more stored heat overall, so the plate stays warm long after the plastic has cooled. And because plastic is cooler than everything around it, it’s the perfect surface for steam circulating inside the machine to condense on. The effect is especially noticeable in dishwashers that use condensation drying, which rely entirely on residual heat to dry.  

Add to that the fact that most plastics are hydrophobic, meaning they repel water, so water pulls itself into beads on the surface. Glass and ceramic are hydrophilic, so water spreads across them in a thin film instead. A thin film evaporates faster than a bead holding the same amount of water. 

So plastic loses on both counts: It cools off faster, and the water sitting on it dries more slowly.

How To Speed Things Along

Rinse aids lower water’s surface tension so it runs off instead of beading, even on plastic. In fact, Whirlpool lists skipping rinse aid as one of the most common reasons dishes don’t dry.

Another option is to turn up the heat. If your machine gives the option, you can choose “Heated Dry” or “Extra Dry” for plastic-heavy loads. On the flip side, skip Eco and Quick cycles, which cut both heat and drying time. 

Loading and Unloading Tips

When loading your dishwasher, keep plastics on the top rack. Leave ample space between items so air has more room to circulate, which will help plastic dry more quickly. 

When the cycle ends, prop the door open slightly so steam can escape instead of settling back onto the dishes. Then, when it’s time to unload, start with the bottom rack — upturned plastic on top (which seems to always happen) can collect water, and pulling the top rack out first would cause spillage onto  the dry dishes below. 

Even with all these tips, some plastic will probably still come out damp. But that’s just physics — and nothing a quick wipe with a dish towel can’t tackle.

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