# Why are the bottoms of plastic bottles shaped like the are?

**URL:** <https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305>\
**Category:** Factual Questions\
**Created:** [April 3, 2003, 9:25pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305 "2003-04-03T21:25:26Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Talking\_Meat\_Puppet](https://avatars.discourse-cdn.com/v4/letter/t/a183cd/32.png) [@Talking\_Meat\_Puppet](https://boards.straightdope.com/u/Talking_Meat_Puppet)\
**Post date:** [April 3, 2003, 9:25pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305/1 "2003-04-03T21:25:26Z")

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You know… The five little out jut thingies, so it stands on 5 little pedestals intsead of on a flat bottem. I’ve always wondered that, because it would seem to take more plastic for that, and probably harded/more complex to make… why bother at all? Why not have a flat bottom?

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [April 3, 2003, 9:50pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305/2 "2003-04-03T21:50:43Z")

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I believe it provides a mechanical connection for the machinery which screws on the caps. The notches fit over complementary fingers on the machine to keep the bottle from rotating while the cap is screwed on.

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**Author:** ![keithnmick](https://avatars.discourse-cdn.com/v4/letter/k/90db22/32.png) [@keithnmick](https://boards.straightdope.com/u/keithnmick)\
**Post date:** [April 3, 2003, 9:55pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305/3 "2003-04-03T21:55:21Z")

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Plus the pressured contenst would cause a flat bottom to bow outwards, and the bottle would then fall down.  
Also the manufacturing technique (blowmolding) prefers a generous radius, and a nice radius on a flat edge won’t be too stable.  
Strength too, perhaps?

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**Author:** ![Von\_Erich](https://avatars.discourse-cdn.com/v4/letter/v/d78d45/32.png) [@Von\_Erich](https://boards.straightdope.com/u/Von_Erich)\
**Post date:** [April 3, 2003, 10:16pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305/4 "2003-04-03T22:16:49Z")

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Didn’t they used to have black caps on the bottom that made it flat? i remember this on Dr. Pepper bottles specifically. I guess that change was to save money.

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**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\
**Post date:** [April 3, 2003, 10:22pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305/5 "2003-04-03T22:22:48Z")

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> [@](#):
>
> Didn’t they used to have black caps on the bottom that made it flat? i

Yes they did and if you pulled off that cap the bottom was rounded. I think it’s a factor of saving money, holding up to pressure and being able to stand up.

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**Author:** ![effac3d](https://avatars.discourse-cdn.com/v4/letter/e/b487fb/32.png) [@effac3d](https://boards.straightdope.com/u/effac3d)\
**Post date:** [April 3, 2003, 11:05pm UTC](https://boards.straightdope.com/t/why-are-the-bottoms-of-plastic-bottles-shaped-like-the-are/166305/6 "2003-04-03T23:05:41Z")

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Yeah but now you can’t make a little greenhouse out of the old bottles :(.

I can’t be the only one that remembers that from elementary school…