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I know that solid materials expand when heated, which is called thermal expansion.

But what is happening to tent square or tent canvas of (plastic?) camping tents? I have noticed, that during the day, when it’s hot, there is a lot of tension in the skin of a tent. But when it gets colder (when raining or during the night), the tension is less and the fabric gets sloppy.

What is the reason?

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    $\begingroup$ I failed to find proper term, so I'll write what I recall from my brief course of polymer science. Polymers, including polymer fibers, consist of long entangled molecules . When under strain, the molecules straightens and the material elongates in direction of stress. When heated, this order is destroyed and molecules once again entangle, shortening the fibers. $\endgroup$
    – permeakra
    Aug 2, 2014 at 5:59
  • $\begingroup$ some more info on the subject en.wikipedia.org/wiki/Rubber_elasticity $\endgroup$
    – permeakra
    Aug 2, 2014 at 6:00
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    $\begingroup$ If the tent poles are made of metal, perhaps they are expanding during the day when it is hot and contracting at night when it is cold. This could increase the tension of the canvas during a hot day and make it loose and sloppy on a cooler night. $\endgroup$
    – theo
    Nov 9, 2014 at 0:29
  • $\begingroup$ theo, consider writing your comment into an answer, I think that explanation is perfectly reasonable given the information. Polymer deformation seems less likely to contribute to this observation significantly. $\endgroup$
    – venture
    Jan 7, 2015 at 19:31
  • $\begingroup$ @theo: To me the effect of elongating tent poles can not explain this, because this happens with every kind of tent poles (aluminium, carbon fiber, …). And if you’ve ever watched a tent, you will notice, that the whole tent canvas is under tension. Also the parts, that have no tent poles inside. $\endgroup$
    – erik
    Feb 19, 2015 at 0:26

2 Answers 2

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The surface of a tent consists mostly of water-resistant polymers such as latex or plastic. These polymers are disordered molecules such as spaghetti, so they have unlike crystals a high entropy.

Gough (1805) and Joule (1859) studied the thermal behavior of rubber. They made the following observations, which are known as Gough-Joule effects: • a taut with constant weight rubber shrinks when it is heated • rubber emits heat when it is stretched

The cause of the rubber elasticity is fundamentally different than the elasticity of crystalline materials. In contrast to a crystal, the atoms are not regularly arranged in a rubber, but they form long chains (polymers) which are interconnected and form a network. Clearly, one can think of it as a plate of cooked spaghetti. This difference in microstructure are reflected in the mechanical properties of rubber. When the rubber network is loose, very many different configurations (configurations) of the chain between two connection points are possible - more disorder (larger entropy S).

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  • $\begingroup$ Does your answer explain, why this happens again and again, every day when the tent is heated it has a high tension, but in the evening, when it gets colder, it has no tension at all. Wikipedia says: The Gough–Joule effect is the tendency of elastomers to contract when heated if they are under tension. Elastomers that are not under tension do not see this effect. In the evening it seems to not be under tension, but when it heats up the tent canvas seems to contract. Maybe this effect is not the reason for this to happen. $\endgroup$
    – erik
    Feb 19, 2015 at 0:20
  • $\begingroup$ When heated up the material shrinks - when cooled the length of the material increases. $\endgroup$
    – Noli-me
    Feb 22, 2015 at 8:13
  • $\begingroup$ When heated up the material shrinks - when cooled the length of the material increases. The tension is given from 2 effects: a) from inside the structure of such a polymer, as the result of the inner energy, given by enthalpy and entropy. b) from outside by the tension due to the weight of the material of the tent, the gravity and from the metal construction that builds the tent. $\endgroup$
    – Noli-me
    Feb 22, 2015 at 8:21
  • $\begingroup$ That Gough in 1805 did his experiments with unvulcanized rubber? $\endgroup$
    – Georg
    Mar 19, 2015 at 22:20
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The air inside the tent heats up and expands, the tent, while not completely airtight still acts like a balloon expanding with the heated air inside it and as the air cools down it shrinks, deflating the tent/balloon.

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  • $\begingroup$ Welcome to chemistry.SE! If you had any questions about the policies of our community, you can ‎visit the help center or take a ‎‎tour of the websit‎e. || I don't have much insight to the problem, but your answer seems misleadingly illogical to me. $\endgroup$
    – M.A.R.
    Feb 17, 2015 at 22:22
  • $\begingroup$ Welcome to chemistry.SE , Tents always let some air interchange with outside, if not, people inside would get out of oxygen, so it can not work as a balloon if it takes a reasonable time to heat the air. $\endgroup$
    – user1420303
    Apr 21, 2015 at 17:18

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