final comments about testing a sleeping bag

HOW A SLEEPING BAG IS MADE ALSO CONTIBUTES TO ITS EFFICIENCY

What I published on Monday concerning the temperature ratings of my bags using the Natick Theoretical Clo chart was incomplete. I did not include the numbers for the systems.

My Ultra-Light plus the overbag is rated to -20 degrees which equates to 8.5 clo.

My Super-Light plus the overbag is rated to -40 degrees which equates to 10 clo.

My Ultima Thule plus the overbag is rated to -60 degrees which equates to 11.75 clo.

My Antarctic bag as a stand-alone is rated to -60 degrees which equates to 11.75 clo.

My Antarctic bag plus the over bag is rated to -80 degrees which equates to 13.25 clo.

For the sake of good order the weights of each bag are shown based upon the long wide body size.

Overbag 3 pounds

Ultra-Light 4 ¼ pounds

Super Light 5 pounds

Ultima Thule 6 pounds

Antarctic bag 8 pounds

I have noted that testing the insulations as stand-alone products will not give good results but if you encase the insulations in the fabrics used to make the sleeping bags offers better results, however when you test a sleeping bag with a human not a manikin you get the best results. Of course having a number of people using the same model bag the same day after participating in the same activity and eating the same food you will get the best results and of course it will be in F temperature, not clo.

While the insulating medium is the most important component of the sleeping bag there are several other factors that play a vital role in the bags ability to keep the occupant warm.

The nylon that I have used for years (over 30) is a 70 denier (thickness of yarn) with a thread count of 86 x 104 yarns per square inch. I think the yarn size is the optimum for strength but more importantly for quickly absorbing the heat that reaches it from your body. If the insulation is doing its job of retaining heat the nylon will not lose much heat and therefore, will not reabsorb heat from your body. Slowing down the conductive movement of the heat also slows the metabolic rate at which you consume the food (your fuel). The spaces between the yarns allow the moisture while still in a vapor state to move quickly away from you. If the insulating medium is Lamilite/Climashield it will not hinder this movement of moist vapor.

The design of the bag is an arc over the top of the body and there is a space that is developed between the shell material and the lining which has some air which further aids the effect of insulation. When air is trapped within the insulating layers of the bag it becomes stagnant and like water that is stagnant it warms. The denser the insulating medium is to a point the more air that is stifled in its movement. One of the actions that companies use in clo testing is having a fan in their testing chamber. Why, if the person using a sleeping bag is in a tent where there is no air movement is this necessary? BLANK! It is widely known that wind moving across a surface pulls the heat away so using the fan during testing makes no sense to me if in an enclosure.

In the information I published by Gagge etal they refer to radiant and convective heat loss, it just does not happen. For a more detailed explanation go to the home page of my web site and scroll down to the article “How to Stay Warm”.

When we were involved in the first Gulf war I received an order from the USMC for 200 sleeping bags which I called the Desert bag (still make them) and they were shipped to Virginia. Since the war ended so quickly the Major who ordered them sent them to 29 Palms, CA. where they were issued to 200 young men all about the same age maybe 20 years old. They were all training at the same place for a month. Therefore, they were all wearing the same clothing, eating the same foods and of course all participating in the same activity. The Major called me and said the bag which I rated then and still rate today as a 40 degree bag performed admirably to a low temperature of 27 degrees. I was not only surprised, but delighted. Imagine trying to get 200 civilians to participate in such a test. To my way of thinking I was just lucky to have been involved with this activity.

While I still sell the Desert bag I also still recommend a low temperature of 40 degrees, so if any who buy it can be comfortable lower than 40 degrees let me know.

As you can see testing a sleeping bag is not cut and dry (of course being in a Wiggy bag is dry). All of the companies that market sleeping bags like to say how this component or that component has been tested and “verified” by some third party who hasn’t any more knowledge of what it takes to make a sleeping than the company paying them for their “verification”. I call this an action of the blind leading the blind!