# Why Does Natural Rubber Harden/Crystallize?

**URL:** <https://boards.straightdope.com/t/why-does-natural-rubber-harden-crystallize/387143>\
**Category:** Factual Questions\
**Created:** [January 8, 2007, 2:12pm UTC](https://boards.straightdope.com/t/why-does-natural-rubber-harden-crystallize/387143 "2007-01-08T14:12:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\
**Post date:** [January 8, 2007, 2:12pm UTC](https://boards.straightdope.com/t/why-does-natural-rubber-harden-crystallize/387143/1 "2007-01-08T14:12:17Z")

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Doing some rewiring in our 84-year old house, I notice that the old wiring is insulated with cloth and rubber. the old insulation is quite brittle-if you bend the wire, the insulation will crack and break off. Why does natural rubber harden like this? is it a chemical reaction with oxygen. or is it a crystallization process?

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**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\
**Post date:** [January 8, 2007, 4:24pm UTC](https://boards.straightdope.com/t/why-does-natural-rubber-harden-crystallize/387143/2 "2007-01-08T16:24:40Z")

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[QUOTE=ralph124c]  
Doing some rewiring in our 84-year old house, I notice that the old wiring is insulated with cloth and rubber. the old insulation is quite brittle-if you bend the wire, the insulation will crack and break off. Why does natural rubber harden like this? is it a chemical reaction with oxygen. or is it a crystallization process?  
[/QUOTE]

It is a reaction with oxygen.