Topic 4:

Overview of Thermal R Insulation Values (CLO) & Why They Are Important:

Whether you buy an existing house or even have the opportunity to build one or more, one of the most important questions that is usually asked is “what is the insulation R-value that’s in this house” or “what are the specifications for the walls and ceiling that we are going to build into this new house”, right?  Why do we ask these questions, or why is the R-Value of the insulation so important?  Well,  because we know that if we have the proper amount of insulation in our walls and ceilings,  it will help in the heating and cooling processes of our homes and perhaps even save us some money on our energy bills, correct?

Interestingly enough when it comes to many of the garments that we use for our outdoor activities, especially those items that we purchase for extreme cold weather activities, this information is “completely” omitted and is left missing.  Sometimes we may be privileged to see a very small tag on a pair of mitts that states that it contains “XX” grams of this or that type of brand named insulation material, but “really”, what does that mean to you?  Lets say that you are in a sporting goods store and you are comparing two different sets of Winter Mitts.  One pair of mitts features an  insulation tag on it from a large manufacturer in the US with say 400 grams of that manufacturers insulation in it and the other pair of mitts either features a tag or some information that just states “down or goose down” insulation, which pair is going to be warmer?  Further, lets say that the two pair of mitts are equally bulky and fluffy in size and appearance and let’s even say that they are selling at the same price, which one do you purchase?  Or lets say that the mitts with the 400 grams of insulation are selling for $50.00 more then the “down” mitts, do you decide to purchase them because they are the most expensive, therefore they have to be better?

The insulation value of anything is certainly very important, but it should be extremely critical when purchasing something that you are going to wear on your hands to keep them warm if you are involved with Winter sporting activities or just going outside in the frigid temperatures to snow blow your driveway for an hour or more at a time.  In the fabric manufacturing industry, especially with those who are involved with manufacturing garment insulation material or technical outdoor fabrics, the unit of measurement for insulation is termed in “CLO” or in layman terms, “units of relative warmth or the thermal resistance of clothing”.  The actual calculation formula that was developed for determining CLO is quite complex, as it deals with the insulation required, based on a certain metabolic rate, at a certain specified temperature, air flow rate and maximum relative humidity and before you could read through the complete formula you would be asleep.  Suffice it to say that for approximation purposes, one CLO unit is roughly equal to one “R” insulation value.(example:  a garment with a CLO insulation value of 5.0, would have an understandable insulation value of “R-5.0”.

The following chart will give you a very brief comparison to some of the “brand name” insulation materials that we are all familiar with, as follows:  

Insulation Material


Material Thickness

Thinsulate CDS 40 gram


0.10 inch

Thinsulate CDS 150 gram


0.40 inch

Thinsulate CDS 250 gram


0.70 inch

Hollofill ll 150 gram


0.84 inch

550 Fill Goose Down


1.10 inch

Thinsulate is a Registered Trademark of 3M Corp.
Hollofill ll is a Registered Tradmark of DuPont Corp.

The amount of insulation or “R-Value” of the mitts that you choose to buy and wear, should be  one of the most important facets in your buying research, unfortunately the market place does not make it easy to become an informed buyer.  It is our hope that  the information that we are providing  will help in making you a better informed buyer or to at least will provide food for thought.


Some of the other factors that are important in purchasing  outdoor Winter mitts, is to make sure that the Outer Shell provides a “thermal” wind blocking attribute, to further extend the insulation benefit of the mitts when they are out in the actual elements.  Moisture resistance and breath ability are other factors that the Outer Shell of a mitt should offer as well,  for protecting and maximizing the total insulating value of the mitts.   Lastly, the inner most layer of the mitt that surrounds the hand should have excellent moisture wicking capabilities, for minimizing premature dampness cooling.  

Any type of garment that you wear can be affected by the forces of physics that are experienced in the real world.  To minimize the impact of these forces on heat loss that can be experienced, the correct balance of technical fabric and technical insulation orientation must be formulated in unison to fight off these noted forces as follows:

The major function of any outdoor garment should be to prevent heat loss, whether it’s conductive, convective or due to the build up of excessive moisture.  Unfortunately the reality is that many garments are designed with “eye appeal” only in mind when they are designed and manufactured, because the main mission is to move volume.  Where the better manufacturers let down in their design and manufacturing processes, is that they decide to cut costs by not using the better “fabric weights” of material that are available from their fabric suppliers(they may use a 100 weight material for the zip out vest for a jacket shell instead of using the fabric suppliers 200 or 300 weight fabric), because it may take 20% to 40% out of the cost of the vest.

When it comes specifically to outdoor mitts, the conductive heat loss process mixed in with the “status quo” design of the mitts that most people wear, makes for a powerful combination that leads to cold hands and fingers, yet we wonder why?  The design of the normal “status quo” mitt is built for flexibility first and foremost and for no other reason!  The enhanced supernatural flexibility allows you to wrap your fingers around anything that you choose and you have the ability to grip whatever it is in your mitt as hard as you want.  It also has trained your hand when the mitt is on, to operate in the “un-natural or contrived” hand position, which we mentioned previously.  The lack of insulation on the bottom side of the mitt, which normally runs only 25 to 50% of the amount on the top half of the mitt,  combined with the forever gripping of something cold during the Winter months, allows us to NOW understand why are hands and fingers are getting cold and it’s from the forces of Conduction.  The conductive heat loss process is magnified when we grip something cold, because the veins in our hands are constricting during the grip due to the pressure of the gripping, while the body is continuing to pump heat to the area to maintain thermal equilibrium, which also results in the production of sweat moisture into the area.

In minimizing the forces of Convection, it is extremely important again to have the Outer Shell of the mitt that is made from a fabric that has 95% to 100%  thermal wind blocking capabilities, is water repellent but still has the technical capability to be highly breathable.  Nylon type material which is predominate on most outdoor Winter mitt outer shells can achieve most of these specifications, except for the “thermal” part of the wind blocking requirement.  Think of building a home and the entire house is shelled on the outside with 1/4” plywood, but no other insulation.  The plywood will block the cold Winter wind to a great extent but cold air still enters in the  house weather you have the heat on or off.  This is really all that the nylon shell does for your mitts, other then also blocking out the rain or snow flakes for this example.  Now take the same house with the 1/4” plywood and add 1” thick sheets of cellotex to the outside of the plywood and you now have a participating amount of “thermal” wind blocking protection for you house in this example.  To finish your house or for the right mitt, you now need to have the proper amount of insulation and that is why Thermal “R” Values are so important to understand.