Apparatus for Testing Thermal Insulation Properties

"How does down work in practice? It's very clever actually. The down is made up of lots of very tiny fibres, and around every tiny fibre (and especially the tips of those fibres) there is some still air: a boundary layer. That still air is what makes down such a good insulator. Synthetic fill tries to copy that, but the long fibres in synthetic fill do not trap as much air as the ends of the down fibres. Synthetic fill still has a long way to go to match down."

Doesnt this imply that using synthetic fibres as wadding limits their efficiency, and that using them as short loose fibres contained by baffles (just like down) would be more efficient. I have some cheap down-style synthetic things that seem warmer than would be expected (but have heavy shells).

Roger –

Thank you! I am very glad to read that you are doing the test. I very much look forward to this series.

Dirk

Hi Alan

> that using them as short loose fibres contained by baffles (just like down) would be more efficient

Well, that would be the right idea, but in practice it doesn't work out because the cheap loose fibre fill is usually much coarser than the tips found in down. So you end up with probably orders of magnitude less tips per volume.
Btw – that's also how the very old kapok insulation worked, similar to down but much heavier.

Cheers

Roger

You said you're using metric R values not Imperial

I thought air pads are speced in Imperial R values

Like the Prolite is speced at R value of 2.2 and is 1 inch thick

Styrofoam from the building store is speced at R 3.9 for 1 inch, which is about 22 in SI R. I would expect styrofoam to have a little more R per inch. Prolite R value must be Imperial.

Very confusing because the symbol "R" is used for both

So, Prolite is 2.2 R metric? That doesn't make any sense.

It's very confusing, because like it says in wikipedia, the term "R" is used for both Imperial and metric so you have to infer from context which one it is.

Sometimes they use the term "RSI" for metric R.

But if my R-19 fiberglass insulation is 3.5 inches, that must be Imperial.

And they said at the building supply store my 3/4 inch styrofoam is R 2.9, that must be Imperial.

Those are closer to the Prolite being R 2.2 for 3/4 inch is Imperial. It makes sense the Prolite would be a little less per inch of loft than styrofoam

Imperial R 3.9 = RSI 0.65 – oops, thanks, we don't do metric here in U.S. : )

Nice work. Justifies my subscription.

David,
You state "…even aerogel only manages 1.76 R per inch in SI units (R-10 imperial). Hard to imagine a Prolite 3 beats aerogel…"

uhhh…as you state:

1.76 R in SI units is R-10, Imperial
The Prolite is R-3.8, also Imperial, as it is a USA item and designation.

In the positive number set, 10 is usually greater than 3.8 … at least in this universe.

Hi guys

I've been up the mountains testing tents and mats, and out of contact.

Let me emphasise: all the figures quoted for mats are SI units. I don't know right now what the R-value is for aerogel, and will need to look it up. Right now I am my daughter's place for dinner on the way home, and not really in 'back on earth' yet.

It was meant to be an Autumn light-weight walking trip with light joggers …. We got ~8" snow on the last night and getting off the mountains via a long backcountry dirt track was 'interesting'. We had the chains on the 4WD for a LONG time. Not quite what the weatherman forecast, but that is totally typical for around here.

Tents and mats survived the experience, so all was well.

Cheers

Glad to hear you are heading safely back to your hobbit hole.

Looking forward to reading the results of your testing of the tents and mats.