# plastic mugs

**URL:** <https://boards.straightdope.com/t/plastic-mugs/18810>\
**Category:** Factual Questions\
**Created:** [May 7, 2000, 6:13am UTC](https://boards.straightdope.com/t/plastic-mugs/18810 "2000-05-07T06:13:02Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [May 7, 2000, 6:13am UTC](https://boards.straightdope.com/t/plastic-mugs/18810/1 "2000-05-07T06:13:02Z")

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I’ve got a plastic mug which [Amazon.com](http://Amazon.com) sent out for free. Being a non-American I’m not quite sure what it’s useful for. (Yes they did ship it overseas - no wonder they’re not making a profit!) The lid has a hole to drink out of, like one finds on take-out coffee, which suggests it’s designed to keep the beverage cold or hot. It says “do not microwave” so I guess it’s not for hot beverages. So it’s just for keeping soda cold? It’s no big deal, but I haven’t found a single use for it and thought I’d check before I throw it away.

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**Author:** ![Dusy](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@Dusy](https://boards.straightdope.com/u/Dusy)\
**Post date:** [May 7, 2000, 6:35am UTC](https://boards.straightdope.com/t/plastic-mugs/18810/2 "2000-05-07T06:35:23Z")

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It’s for hot stuff. Coffee while you’re driving to work.

The reason you can’t microwave is the expanding gas in the liner pocket would break the seal. It’s not a vacuum but just an air inuslator. If the seal breaks, water gets into the pocket when you wash the cup, and dribbles down your blouse when you next drink from it.

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**Author:** ![ChiefScott](https://avatars.discourse-cdn.com/v4/letter/c/58f4c7/32.png) [@ChiefScott](https://boards.straightdope.com/u/ChiefScott)\
**Post date:** [May 7, 2000, 8:24am UTC](https://boards.straightdope.com/t/plastic-mugs/18810/3 "2000-05-07T08:24:06Z")

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These mugs are also _de rigueur_ for sailors at sea.

Drinks must be carried in covered cups to prevent spilling them onto heaving decks and possibly causing a “slip and fall.” The larger the cup the better, as these require fewer trips to the mess for refills.

Additionlly, this is one source a sailor can be an individual aboard ship. Popular mugs include pro football teams, college/high schools or hometown coffee joints. I myself carry a Dead mug.

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**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [May 7, 2000, 11:56am UTC](https://boards.straightdope.com/t/plastic-mugs/18810/4 "2000-05-07T11:56:08Z")

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> [@](#):
>
> \*\*  
> It’s for hot stuff. Coffee while you’re driving to work.  
> \*\*

Thanks, that answers my question. I’m still curious about the reason for “do not microwave” though. I didn’t think air was efficiently heated by microwave ovens - only water. Does the insulating layer of air really expand that much?

I wonder if there’s also a layer of plastic coated with metal? If so, that would explain why you shouldn’t microwave it.

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**Author:** ![starfish](https://avatars.discourse-cdn.com/v4/letter/s/87869e/32.png) [@starfish](https://boards.straightdope.com/u/starfish)\
**Post date:** [May 7, 2000, 4:23pm UTC](https://boards.straightdope.com/t/plastic-mugs/18810/5 "2000-05-07T16:23:43Z")

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It could be that the plastic will get hot, and possibly melt. Lots of plastics have the same warning.

Also, you would be surprised at the number of people who, being used to hot coffee in a mug, will grab it out of the microwave, forgetting that the mug is now just as hot as the coffee.