# Theory behind insulation **URL:** \ **Category:** Factual Questions\ **Created:** [November 6, 2024, 4:14pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794 "2024-11-06T16:14:53Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 6, 2024, 7:01pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/21 "2024-11-06T19:01:32Z")
If you don’t want to use straw, you could use sod: [https://nebraskastudies.org/en/1850-1874/the-challenges-of-the-plains/living-in-a-sod-house/](https://nebraskastudies.org/en/1850-1874/the-challenges-of-the-plains/living-in-a-sod-house/) ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 6, 2024, 7:02pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/22 "2024-11-06T19:02:49Z")
Let me give another example. Would dense Styrofoam work better or worse than less dense. Would there be an optimum and how could I mathematically arrive at that. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [November 6, 2024, 7:09pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/23 "2024-11-06T19:09:48Z")
> [@Crafter\_Man](#): > > As a practical point, there’s also the issue of moisture. If the insulation is damp for whatever reason, it will lose its effectiveness. How contained would a moist straw wall have to be to exhibit spontaneous combustion? (presuming it’s between something like two brick walls tat prevent evaporation or significant loss of heat) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 6, 2024, 7:11pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/24 "2024-11-06T19:11:31Z")
I’ve never heard of it happening. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 6, 2024, 7:12pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/25 "2024-11-06T19:12:01Z")
Just compare R-values/inch thickness. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [November 6, 2024, 7:15pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/26 "2024-11-06T19:15:47Z")
> [@md-2000](#): > > How contained would a moist straw wall have to be to exhibit spontaneous combustion? A quick Google search shows it’s pretty rare for wet straw to spontaneously combust (unlike hay). Thank goodness for modern insulation. 🙂 ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 6, 2024, 7:19pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/27 "2024-11-06T19:19:36Z")
> [@Crafter\_Man](#): > > A quick Google search shows it’s pretty rare for wet straw to spontaneously combust (unlike hay). > > Thank goodness for modern insulation. I would think that methane would have to be present for that to happen. The bacteria that causes the heat starts to die off below 160 degrees. I know it has happened, and I have always wondered about the exact circumstances that allowed it to happen. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [November 6, 2024, 7:23pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/28 "2024-11-06T19:23:52Z")
I don’t think regular ol’ Styrofoam (expanded polystyrene or EPS) is used much in construction nowadays. Extruded polystyrene (XPS) has a number of advantages over it. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 6, 2024, 7:25pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/29 "2024-11-06T19:25:54Z")
I am not doing anything with insulation an hour from now I won’t even be thinking about it. I am just curious about the science behind it. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [November 6, 2024, 7:26pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/30 "2024-11-06T19:26:37Z")
Google thermal conductivity. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [November 7, 2024, 1:02am UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/31 "2024-11-07T01:02:31Z")
> [@thorny\_locust](#): > > I have a friend who’s a farmer and a historian and she always gets annoyed at depictions of 1700’s and most-of-1800’s scenes that show hay bales in them. Stooks. Stooks of hay or straw. As seen on the Saskatchewan Coat of Arms: > **[Coat of arms of Saskatchewan](https://en.wikipedia.org/wiki/Coat_of_arms_of_Saskatchewan)** > > The coat of arms of Saskatchewan, officially known as His Majesty's Arms in right of Saskatchewan, is the heraldic symbol representing the Canadian province of Saskatchewan. > The arms, consisting of only the shield, was assigned by royal warrant of King Edward VII on 25 August 1906. It uses the provincial colours, green and gold. The remainder of the coat of arms was requested by the province in 1985, Saskatchewan Heritage Year, and was granted by royal proclamation of Queen Elizabeth II on 16... ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [November 7, 2024, 4:21am UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/32 "2024-11-07T04:21:32Z")
> [@Napier](#): > > Or, you can lower the pressure of the gas, which increases the mean free path. You have to lower the pressure a _lot_ before it matters. At 1/1000 of an atmosphere, the mean free path of nitrogen at 22 C is only 0.07 mm–still way too small to make a difference in most circumstances. The thermal conductivity of air is thus almost constant until you get to very low pressures, like a millionth of an atmosphere. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [November 7, 2024, 3:38pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/33 "2024-11-07T15:38:14Z")
> [@Dr.Strangelove](#): > > You have to lower the pressure a _lot_ before it matters This depends on the size of the voids. If you’re making a thermos type bottle, you need quite a good vacuum. But if you have some kind of powder insulation with really small voids, atmospheric pressure is good enough. For any insulation there’s a level of vacuum that enters this Knudsen regime, and plenty of insulations are practical to do this with. There’s a kind of prefabbed insulation that comes in panels with aluminized plastic sheet covering, filled with fine insulation and evacuated low enough to take advantage of this effect. The stuff has an uncannily low thermal effusivity – hold it in your hand, and it feels warm almost instantly. ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [November 7, 2024, 4:12pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/34 "2024-11-07T16:12:02Z")
Anorher form of construction from olden times is rammed earth. Great for thermal mass, not as good for insulation. Rammed earth is an ancient construction technique that’s been revived in recent years for its sustainability and aesthetics. It’s a load-bearing material that can be used to build walls for houses, museums, and cemeteries. Rammed earth provides: - **Thermal mass** : Rammed earth provides excellent thermal mass. - **Durability** : Rammed earth is very strong in compression and can be used for multistory loadbearing construction. - **Low maintenance** : Rammed earth is low maintenance. - **Fire proofing** : Rammed earth is fire proof. - **Pest deterrence** : Rammed earth deters pests. Rammed earth works best in humid environments with moderate temperatures. In cold climates, rammed earth walls require additional insulation, and in areas with high rainfall, the walls need extra protection from the rain. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 7, 2024, 5:01pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/35 "2024-11-07T17:01:57Z")
> [@smithsb](#): > > with high rainfall, the walls need extra protection from the rain. I have always been fascinated with ram earth construction but never could figure out how they kept it from absorbing water or being washed away gradually. Does the compacting mitigate a lot of the moisture problems? Does it require clay soil or other specific types of soil? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 7, 2024, 5:24pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/36 "2024-11-07T17:24:47Z")
There’s usually a roof. ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [November 7, 2024, 10:44pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/37 "2024-11-07T22:44:45Z")
Another ancient construction related to insulation. Ice storage in the midleast. A Yakhchal, a pyramidal structure. > ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [November 7, 2024, 10:57pm UTC](https://boards.straightdope.com/t/theory-behind-insulation/1009794/38 "2024-11-07T22:57:08Z")
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