TechnoWeenie Educational Series - Insulation

[TechnoWeenie]

Intro..
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Here I'll go over the basics of insulation. This is designed to be a general guide, and won't cover every aspect.

There are other things to consider, like condensation, water vapor, thermal breaks, etc. that will come into play. You'll find that insulation needs will vary based on climate, and there's no 'one size fits all' when it comes to what's needed.

Insulation is rated in R value. The higher the value, the greater the resistance to change in temperature.

I will not be covering things like Denim, or Thinsulate, as they're their own beast.

Let's start out with the basic stuff, that everyone knows about...

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Fiberglass
R2.9-R3.8 / Inch

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Fiberglass is what you'll find in the walls of the boxes on military vehicles like the M109, M934, M820, and M1010. It's a very basic material, easy to work with, and dirt cheap.

Pros

• Cheap
• Easy to use

Cons

• Retains water
• Loses R value over time
• Proper PPE is required

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Cellulose

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Cellulose is designed for loose fill, and should not be used in an automotive application. The vibration will cause settling, and it is a moisture sponge. DO NOT USE. I'm not gonna cover the pro/con because it shouldn't even be considered.

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Extruded Polystyrene (XPS)
R5 / Inch


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Extruded polystyrene is your familiar pink panel that you can pick up at your local hardware store. It's VERY easy to work with, and can be cut to virtually any shape or size. It comes in both standard panels, and foil backed panels.


Pros

• Less expensive than Poly-Iso
• Easy to use
• No PPE required
• Mold/Mildew resistant
• Higher R value than fiberglass and EPS
• Stable R value
• Will not collect moisture, can act as vapor barrier
• Extremely low weight

Cons

• Not designed for sunlight exposure, will degrade material. (If it's in a wall, this isn't an issue)
• Flammable. Temps above 250*F will cause it to melt.
• More expensive than fiberglass

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Expanded Polystyrene (EPS)
R3.5-R4 / Inch



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EPS is very similar to XPS, so the Pros/Cons are virtually identical, but it does differ in a few ways.

• EPS is less dense than XPS, and as such, weighs less. This also gives it a lower R value
• EPS can retain up to 4% moisture, vs the XPS which can absorb less than .3%
• EPS cannot be used as a vapor barrier
• EPS is about HALF the cost of XPS
• EPS is generally MORE flammable than XPS

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Polyisocyanurate (Poly-Iso)
R7 - R8 / Inch





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Poly-Iso is generally regarded as one of the better insulation methods, but in mobile environments, it has some issues. One of the many issues, is the lack of cold weather performance. Poly-Iso will lose it's R value as temperatures drop. An R5 XPS panel will actually outperform an R7 Poly-Iso panel, when below freezing. If you're planning on running a rig in a cold environment, this might not be the best bet.


Pros

• Highest R value of rigid foam board
• Easy to use
• No PPE required
• Higher R value than fiberglass, EPS, and XPS
• Not very flammable
• Excellent hot weather performance

Cons

• Loses R value in cold.
• Readily absorbs moisture - can get waterlogged if wet.
• Most expensive rigid insulation board

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Polyurethane (spray) foam
R6.5 / Inch





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Polyurethane foam is a relatively new thing. The nice thing about spray foam, is that it covers EVERYTHING. The bad news is, it covers EVERYTHING. It can provide a vapor barrier if the proper thickness, and prevents thermal transfer due to small cracks or openings not covered by rigid foam. It's also VERY rigid, and can provide additional structural support.





Pros

• Can easily fill cracks and holes
• Can create an air tight seal
• Higher R value than EPS, XPS, and fiberglass
• Water resistant
• Mold/Mildew resistant
• Not very flammable
• Adds to structural rigidity
• Longest lasting
• Stable R value

Cons

• Generally not a DIY project (kits do exist)
• Ridiculously expensive
• Requires proper PPE
• Requires a cure time, which can be months, to offgas properly.

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Stacking (mixing of products)
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Stacking of products is possible, where needed, however it's usually a compromise. For example, let's say you wanted the superior heat rejection of Poly-Iso, but the cold weather performance of XPS, you could use a layer of each, with a barrier in between. However, this would give you only a marginal increase in each area, and the added expense and difficulty is generally not worth it...

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[TechnoWeenie]

Vapor Barrier




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A vapor barrier is one of those things that not a lot of people know about, or may have heard of it but don't fully understand it.

It's actually quite simple.

A vapor barrier is designed to prevent the transfer of moisture. Generally, you want to keep moisture out, while allowing what moisture does get in, have a path to get out.

Too much vapor barrier, and you end up trapping moisture. Not enough, and you have a ton of moisture make its way inside.

With most walls of your camper box, RV, etc being metal or fiberglass, they already act as a vapor barrier. Adding MORE to the walls could actually trap moisture, causing rust issues with steel frames, trapped water if you get a leak, moisture from propane appliances to build up and get trapped, etc.

Burning propane puts moisture in the air!

For every 1 gallon of propane you burn, you put approximately 1 gallon of water vapor in the air. Whether you use it as heat, either blue flame, or a buddy heater, your stove, or fridge, if it's not vented outside and has a closed ignition source, you're putting water into the air!

A typical 20 gallon propane tank has 4.7 gallons of propane in it. That means you're putting 4.7 GALLONS of water into the air. Similar to dumping a 5 gallon bucket of water!

Ventilation is the key, in terms of RV/Camper conversions. Get the air flowing through.

A place where a vapor barrier would be good to use, is on the flooring, if not otherwise sealed from the elements. This would prevent moisture from coming up from below and rotting the boards. This is why so many older RVs and travel trailers have rotted floors. They weren't built with a moisture barrier on the floors.

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[TechnoWeenie]

Often misused products
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There are quite a few products that are misused....

Reflectix..


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Reflectix is a metallicized film merged with bubble wrap, that's designed to act as a reflector and air barrier. This product needs an air gap to work properly. If it's directly attached to metal, or other surface, it will conduct thermal energy. I've seen so many people tape it to a window, or a wall, making the product virtually useless.


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Foil Tape




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Foil tape is not an insulator. It has quite a large number of uses, but insulating is not one of them. In fact, it's a good conductor of thermal energy. Using foil tape to adhere materials to a wall can actually make things worse, as the tape can act as a thermal bridge.

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