6. Insulated Mugs and Thermos Bottles (Lose Insulation)
Why it’s bad: Many insulated mugs and thermoses have a vacuum seal between two walls of metal or plastic. The high heat can break the seal, ruining the insulation.
The damage: The mug or thermos will no longer keep drinks hot or cold. Condensation may form on the outside. The seal may be permanently compromised.
What to do instead: Wash by hand with warm, soapy water and a bottle brush. Rinse thoroughly. Dry with a towel.
Pro tip: Check the manufacturer’s instructions. Some high-end brands (like Yeti) claim their products are dishwasher-safe, but hand-washing extends their life.
7. Copper, Bronze, or Brass Items (Discolor)
Why it’s bad: The harsh detergents react with these metals, causing discoloration, tarnishing, or pitting.
The damage: Dark spots, greenish film, or uneven patina that is difficult or impossible to remove.
What to do instead: Wash by hand with warm, soapy water and a soft cloth. Rinse and dry immediately. Use a specialized metal polish to maintain shine.
