Can You Put Plastic in the Dishwasher? The Rules That Actually Matter

You stack the kids’ cups, the takeout containers, and the lunch box lids into the dishwasher, and three loads later half of them are warped beyond use. Can you put plastic in the dishwasher — yes, but only certain plastics, on the right rack, on the right cycle. The dishwasher symbol on the bottom of a container is not just a courtesy mark. It tells you whether that item can handle the 140 to 170°F wash and dry temperatures without warping, leaching chemicals, or releasing softeners into the steam. Here is what the symbols mean, which plastics are safe, and the rules that keep your gear usable.

How Hot Does a Dishwasher Actually Get?

A typical residential dishwasher runs the wash cycle at 120 to 140°F and the sanitize or heat-dry cycle at 155 to 170°F. Premium models with steam cycles can briefly hit 180°F. The drying element above the lower rack runs hotter — sometimes 180 to 200°F at the heating coil itself.

That heat is brutal on certain plastics. Polystyrene starts deforming at 200°F, polyethylene at 230°F, polypropylene at 250°F. Heat-soaked over a full cycle, even plastics rated for those temperatures can warp at the edges or develop stress cracks where they contact metal racks.

The Dishwasher-Safe Symbol

The official dishwasher-safe icon is a small square with water droplets or wavy lines beneath plates or glasses. It appears stamped or molded into the bottom of a container. Some manufacturers add “top rack only” text or a small “T” next to the icon.

If there is no dishwasher-safe symbol at all, assume the item is not safe. Hand wash. Many imported containers and older plastic items lack any safety markings because they were manufactured before the symbols were standardized or because they are not dishwasher-safe but the manufacturer did not bother to mark them.

Plastics That Are Generally Dishwasher-Safe

Five plastic types tolerate dishwasher cycles when manufactured properly.

• Polypropylene (PP, resin code 5) — Tupperware, Rubbermaid, many food storage brands. Top-rack safe in most cases
• High-density polyethylene (HDPE, resin code 2) — milk jugs, some food containers. Generally safe top rack
• Polyethylene terephthalate (PET, resin code 1) — water bottles, soda bottles. Most single-use PET is NOT dishwasher safe
• Tritan copolyester — used by Camelbak, Nalgene, OXO. Specifically designed for dishwasher use
• Silicone — bakeware, lids, baby plates. Always dishwasher-safe

Plastics That Should Never Go in the Dishwasher

Three plastics consistently fail in the dishwasher. Polystyrene (PS, resin code 6) including styrofoam cups, takeout containers, and disposable cutlery — these warp into useless lumps. Polyvinyl chloride (PVC, resin code 3) which includes some cheap toys and food wraps — heat releases plasticizers.

Polycarbonate (PC, often code 7 or unmarked) — the old hard-clear plastic baby bottles and water bottles. These contain BPA which leaches at higher rates in heated dishwashing cycles. Most modern polycarbonate has been replaced with Tritan or PP, but old containers in the back of the cabinet may still be polycarbonate.

Why the Top Rack Rule Exists

The heating element in most dishwashers sits at the bottom of the tub, under the lower rack. The lower rack runs 15 to 30°F hotter than the upper rack during the dry cycle. Most dishwasher-safe plastics are rated for top-rack use only because they cannot survive direct heat element exposure.

If your dishwasher has a hidden heating element (most modern Bosch, Miele, and KitchenAid models hide it under the tub floor), the temperature differential between racks is smaller — but you should still default to top rack for plastic until you confirm your model runs cool enough.

How to Test a Plastic Before Committing

If a container has no symbol and you cannot find product info online, do a single-cycle test before committing your full collection. Place one piece on the top rack, run a normal cycle, and check after the dry cycle finishes. Look for warping, cloudiness, stress whitening (a milky tint where the plastic stretched), or any softening at thin edges.

One pass usually reveals the answer. If it survives one cycle looking fine, it will probably survive long-term — though plastics gradually degrade with repeated heating regardless of safety rating, so even safe plastics eventually need replacing.

Reusable Water Bottles: A Special Case

Stainless steel bottles like Hydro Flask, YETI, and Owala are technically not plastic, but they often have plastic lids that fail in the dishwasher. The vacuum-insulated body usually says hand-wash because dishwasher heat can damage the seal between the inner and outer walls.

Tritan bottles (Camelbak Eddy, Nalgene OG) are explicitly dishwasher-safe top rack. Their lids and gaskets usually are too. Plastic bottles with rubber gaskets and silicone valves need disassembly before washing — pull every removable part and place them in the silverware basket.

Cycle Choice Matters as Much as Plastic Choice

Even safe plastics last longer on shorter, cooler cycles. Skip the heated dry whenever possible and use the air-dry or “energy saver” option. Skip the sanitize cycle for plastic loads — it runs hotter than necessary for anything other than baby bottles and cutting boards.

For mixed loads with both plastic and metal cookware, run a normal wash with heated dry off. Plastic warping mostly happens during the dry cycle, not the wash. Open the door at the end of the wash cycle and air-dry instead.

When in Doubt, Hand Wash

Plastic items you love (the lunchbox, the favorite mug, the kids’ bowl) deserve hand-washing. Five minutes at the sink protects items that cost $15 to $40 to replace. The can you put plastic in the dishwasher question really comes down to: how much do you trust the manufacturer’s labeling, and how much do you want to risk that specific item?

For everyday plates, cups, and Tupperware where you have backups, the dishwasher is fine if the symbol is present. For irreplaceable items, hand-wash and skip the gamble entirely.