EN Ratings and R Values; how do these align?

[Jerry Adams]

I’ve measured similar a number of times, that was just one that I wrote down.  It was at a developed campsite so the ground was compacted, mostly rocky, with a little duff but definitely not heating up from composting.  Thermarest Pro which has an R value of about 2.5

You guys should try that, you might be surprised : )

The first measurement was just after I put the pad down – I wanted to get the temperature of the ground.

The second measurement was in the morning (before the sun came up).

The same effect happens with adobe houses.

The ground has both thermal mass and insulation.  The thermal mass means it takes a while to heat up.

I can estimate the R value of the ground insulation.  If the ground temp was 49, and it was 64 next to my pad that’s a 15 F difference.  It must have been about 94 F between the pad and my body, so that’s a 30 F difference, twice as much.  The effective insulation of the ground must be half the R value of the pad, so the insulation provided by the ground is about R = 1.25

[Michael Glavin / Zenbivy]

All: I have confirmed that the R value of the mattress used in the EN test is actually 5.09~5.87. (this is “accurate”, while realizing the deficiencies of R value measurements)

The real bombshell of all of this, as suspected, is that most folks don’t realize that the bag they are buying will not meet the temperature rating they think, because there is an overwhelming chance that the pad they use will be the weak link. And based on the data above from eric chan (mccullough study), the deficiency is significant.

The challenge for ZENBIVY (and all brands, really) is that we want to make a solution for folks that not only works the way we intend, but allows them to make an informed choice about how the product will perform for them.

The EN rating system endeavors to do just this, but because it only tests one element of the system, while a KEY element of the system, the pad/mattress, is part of the standardized test. And that key part offers thermal performance that far exceeds that of average products in the market.

The real “problem” is that folks have to (get to) choose the right bag and pad for them, in effect creating thousands of combinations without any real way to determine what the thermal performance of their system will be.

So here is what I am going to do. Let me know what you think about this:

1. Use R value for the mattress. Even though it has deficiencies, it is the only information currently available to consumers.

2. Test our sleeping system with several pads/mattresses of known R values, according to the EN protocol. In other words, we are going to change one of the standards, the pad/mattress, to determine the effect of different mattresses on the final temperature rating.

3. the results can be graphed, and show the customer the effect of R-value on the temperature rating. So you can just find the R value for your mattress on the chart, and determine the corresponding EN rating.

4. this will also allow geeks like us to start to answer the question about where the best investment of weight is. I strongly suspect that a 3 pound system with a 2 pound bag and a 1 pound mattress will often be significantly colder than a 3 pound system with a 1.5 pound bag and a 1.5 pound mattress, even though the 1.5 pound bag would have a much lower EN rating.

This is actually the testing that I was already planning, and this discussion confirms that it is necessary to get the information I am needing….

[James holden]

or everyone could just …

1. use a neo air xtherm …
2. use a synthetic bag/quilt and a pad with r ~4 …

which basically solves the issue

the en-rating gap with insufficient pads has been discussed on BPL for at least the last half decade or so, if not longer

;)

[Michael Glavin / Zenbivy]

Matt:

One ancillary thought on the humidity management of down:

Most people I know agree that down is more comfortable than synthetic because it controls the humidity of the microclimate much better, as you suggest.

There are several factors, obviously, including the MVTR and air-permeability of the down-proof fabric, but lots of anecdotal evidence suggests this is true. This also helps explain why your down jacket is so comfortable in such a super-wide range of temperatures compared to synthetic.

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