We have an online forum for our vanlife community to share ideas and experiences around using Havelock Wool. Every so often there is a post that we just have to share with our whole community, even if you’re not a vanlifer. The below from Jillian Serenity is a succinct and simple explanation of the physics of energy transfer, how different types of insulation respond, and how it all relates to a crucial component of any structure… moisture management.

It is important to understand the basic physics of energy transfer and how different types of insulation are designed to work in response to these.

Generally speaking, there are three ways to transfer energy:
1) conduction (touching the burner on your stove and feeling it burn you)
2) convection (boiling pot of water, or weather)
3) radiation (light from the sun, or heat you “feel” on your face from a campfire)

The first two require a medium to work (the second requiring a fluid medium). The third is the only way to transfer energy in a vacuum (like how the sun transfers energy across the near-vacuum of space to heat the earth’s surface).

Reflectix “reflects” light (radiation), preventing that radiation from converting into heat absorbed within the van. It is well suited for windows, where you are trying to reflect solar radiation from coming in.

Heat in your walls comes in via conduction. You cannot, with much efficiency “reflect” the heat coming in through your walls via conduction (technically with a proper air gap you may be able to reflect some infrared “heat” radiation from the reflectix back to the metal skin of the van, but it’s not going to gain you much). In contrast, wool sits over the skin of the van creating a non-conducting barrier between the inside and the skin.

You can do this experiment yourself. Start by touching “exposed” skin on your van wall or ceiling on a hot day. It’ll be quite warm. Now touch a section with a layer of the wool. You will see that it feels much much cooler to the touch (assuming you have a proper-sized layer in place).

Now, with a layer of reflectix against the skin, you can verify by touching it that it too will be quite warm. If you layer it over the wool, you will not experience much of a temperature difference compared to the temp of the bare wool.

So you can then conclude that the cost vs benefit won’t be worth it. In addition, as many have pointed out, it will create a moisture barrier – old wisdom is that you want moisture barriers in vans – but this has been shown to backfire because inevitably a moisture barrier ends up trapping moisture in and not letting it back out. So modern approaches to building vans is to allow them to breathe as much as possible.

Yes, absolutely use reflectix. But use it as it was intended. I sincerely don’t mean this to sound rude, it’s just a matter of fact – those who layer reflectix on their walls or under their floor simply don’t have an understanding of the basic physics of energy transfer. It’s a waste of time and money and can lead to more problems (with respect to moisture management).


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3 comments on “Energy Transfer 101

  • If it were not for Hobo Ahle’s “Building A Van Home” Youtube series — several videos stressing (and demonstrating) the value of wool for insulation — I probably would never have known about wool for my van. But I’m SO glad I do! I’ve put Havelock wool everywhere I can, and it really is great. It’s been keeping out the heat of the summer sun very well. And I’m surprised how outside noises are now almost non-existant as well. Thank you Hobo Ahle, and thank you Havelock. LOVE YOU GUYS!!

  • It’s amazing how some don’t realize it and argue that reflectix everywhere does the job.
    I got a passenger van got reflectix on all the windows around and if heat gets in the reflectix keeps it there.

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