Oh, the promise that a plastic cup labeled “top rack dishwasher safe” keeps! Carefree kitchens with glasses that are not only unbreakable, but also dishwasher safe. No more piles of plastic items waiting to be hand washed. An escape from tedium… relief from monotony!

Indeed.

Clear plastic cups that don’t stain in the dishwasher are certainly a reality for some. But anyone with a dishwasher less than ten years old may have a different opinion. Your “top rack dishwasher safe” glasses often come off the top rack cracked, flaky, or cloudy, sometimes after only a few wash cycles. What gives?

For those who are quick to point the finger at plastic cup manufacturers for mislabeling their products, brace yourselves. It’s not the plastic cups that are faulty, it’s that dishwashers have come a long way in the last decade, mainly due to the EPA’s Energy Star guidelines for energy-efficient appliances.

Most dishwashers made before 1994 draw hot water directly from a home’s water heater, which is typically set to 140 degrees F or so. Although too hot for most household needs, 140 degrees is the optimal cleaning temperature recommended by most dishwasher detergents, and it won’t harm most top-rack dishwasher-safe plastic cups.

Newer Energy Star rated dishwashers feature built-in water heaters that further heat the wash and rinse cycle water by up to 30 degrees. Since the incoming water no longer needs to be as hot, home water heaters can be turned down to 115 or 120 degrees to save energy, which is fine for other home uses.

Unfortunately, home water heater settings are often overlooked when installing a new dishwasher. And while a 30-degree rise doesn’t sound like much, it can be enough to break the heat tolerance of many dishwasher-safe plastics.

But there are ways to enjoy the benefits of newer dishwashers without giving up the convenience of plastic dinnerware.

Those with Energy Star rated dishwashers should first refer to their owner’s manual for water setting temperatures. If possible, wash plastic tableware in an unheated environment so that the incoming hot water does not overheat. If there is no non-heat option, check the home’s water heater. If you set it to around 140 degrees, turn it down to 120 degrees, so that the final temperature of the water in the dishwasher doesn’t go above 150 degrees.

For drying, the air dry setting is generally best for extending the life of plastic dinnerware, as hot drying temperatures can be excessive for many plastics.

Finally, not all plastics are created equal: some plastics work much better in all types of dishwashers than others.

For long-lasting good looks, glasses and plates made of heavy-duty plastic such as melamine, SAN, polypropylene, or polycarbonate are better choices than items labeled “top rack,” which are typically less durable acrylic or Styrofoam. Dinnerware made from these higher-quality plastics is often found in busy restaurants, as it can withstand repeated washing in commercial dishwashers up to 155 degrees.

Best of all, most restaurant-quality plastic dinnerware is dishwasher safe on any rack. Now, that’s convenience for singing.