thermal clothing conductivity rating Polypropylene will keep you warm and dry because it has the lowest thermal conductivity of any traditional apparel fabric. Thermal conductivity is the measurement used to determine the rate at which heat (from your body) is transferred through the fabric to the outside where it is lost. A lower thermal transfer rate is a better because it means heat will be lost over a longer period of time. Polypropylene has the lowest body heat or thermal conductivity of any traditional apparel fabric including silk, polyester and wool.


The U.S. Military chooses polypropylene as their cold weather base layer of clothing and for good reason. Military Thermals not only keeps you warmer and dryer, but Military Thermals even at expedition maximum weight is thin, light (9.5 oz – Large), and does not have the bulk of other materials such as wool that would be required to provide the same warmth. This combination of thermal efficient fabric and weight, gives you more freedom of movement while maximizing warmth. Polypropylene is ideal for under work clothing and for outdoor sporting activities like hiking, biking, fishing and camping just got more enjoyable when you are warm.



    $14.99 Add to cart

    $14.99 Add to cart

    $14.99 Add to cart

    $14.99 Add to cart


Military Thermals comply with the US Military’s Battle Dress Uniform (B.D.U.) standard of sizing. As such, there are some size characteristics to be aware of. The sleeve length tends to run short, by design. The purpose of leaving the sleeve length shorter is to ensure that layered clothing does not start to stack up at the cuff. The thermals, being the base layer, have the sleeves terminate higher on the wrist to leave room for the outer layers. If you would like your sleeves a little longer, consider purchasing one size larger. If you would like your sleeves a little longer, consider purchasing one size larger.
thermal pant sizing thermal crew sizing


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Military Thermals is able to provide a superior product at a tremendous value. As a result we offer minimal phone support.
Emails will frequently be answered within 1 hour however it will never be longer than 1 business day.
E-mail: Phone: (260) 267-0078



Polypropylene clothing should be washed in cold or warm water and hang to dry, or VERY LOW dryer heat. Polypropylene, being a plastic polymer, has a low melting point and care should be taken to keep the material away from high heat or open flames. To maintain your clothing’s hydrophobic properties, do not use fabric softeners or dryer sheets on polypropylene fabrics or put in the dryer with heat. For best results, wash in cold, or warm water and hang to dry. Polypropylene is designed to be the best extreme cold base layer of clothing worn next to your skin. No other fabric is more suited for the job. Polypropylene is not the most stable fabric worn on the outside. In the presence of UV rays polypropylene may fade over time. Polyester is a more stable fabric for outer layers and its ability to repel water. A layered combination of Military Thermals Polypropylene and a Polyester shell is your best combination for extreme cold weather comfort.


Polypropylene is a thermoplastic polymer used in a variety of applications, including as a base layer in the first generation of the ECWCS (Extended Cold Weather Clothing System). The ECWCS was developed by the United States Army as a protective clothing system. The system used a triple layering system to created an insulated platform to maintain a soldier’s mobility and survivability in extreme environments. The entire system consisted of 22 total items from base layer to exterior parka including gloves, socks, boots, etc.
The original Gen 1 Extended Cold Weather Clothing System (ECWCS) was upgraded to the second generation to improve limitations of the parka fabric which did not breathe well and as such created limitations for the system as a whole in the field. The second generation, Gen 2 ECWCS included two different layers made with Polartec® fabrics: the Polartec Classic 300 shirt and the Polartec Classic 200 overalls. The parka was improved with vents to help deal with the condensation problems created by the waterproof parka material.
Third Generation, Gen 3, Gen III, ECWCS was a substantial change from the prior two generations, featuring 7 new layers of insulation. Three of these new layers are Polartec fabrics; two layers of Polartec Power Dry® and a layer of Polartec Thermal Pro High Loft®. With these changes brought additional expense to the system as a whole, specifically to the lighter weight, higher cost Polartec base layers.
These new Gen 3 Polartec base layers do preform their function better within the confines of the system for which they were designed to operate. Do they perform equally as well outside of the ECWCS? We think they do not. The original Gen 1 polypropylene thermal underwear is in our opinion the best performing and most comfortable product to be worn for everyday use as thermal underwear outside the confines of a miliary survival system. Many of our armed service men and women still prefer Gen 1 polypropylene and many military procurement specialist purchase our product to serve this demand.
In recent years polypropylene fabric has been exceedingly difficult to find; impossible if you were searching for a made in the USA product. The immediate solution was a Chinese produced alternative. Frankly, it’s not a bad option and one that even we were forced to embrace while searching for an alternative solution. Many brands you may be familiar with like the Bass Pro RedHead E.C.W.C.S. claim to be “military fleece thermal” and they are not. These products and others like them are produced with polyester, not genuine polypropylene. Polyester is stiff and not nearly as soft and comfortable as polypropylene. You really can feel the difference.
Military Thermals is proud to produce our own brand of genuine US Mil-Spec Gen 1 thermal underwear at our offices in Fort Wayne, IN. Military Thermals brand polypropylene thermal underwear are produced with 100% materials made in the USA and with 100% US labor. Military Thermals are 100% made with pride in the USA!
The density of polypropylene is between 0.895 and 0.92 g/cm³. Therefore, polypropylene is the commodity plastic with the lowest density. With lower density, moldings parts with lower weight and more parts of a certain mass of plastic can be produced. Polypropylene is normally tough and flexible. Polypropylene has good resistance to fatigue.
Polypropylene is at room temperature resistant to fats and almost all organic solvents, apart from strong oxidants. Non-oxidizing acids and bases can be stored in containers made of polypropylene. At elevated temperature, polypropylene can be solved in of low polarity solvents (e.g. xylene, tetralin and decalin). Polypropylene in conjunction with carbon black provides protection from UV attack.
Polypropylene is highly colorfast and is widely used in manufacturing carpets, rugs and mats to be used at home. Polypropylene is widely used in ropes, distinctive because they are light enough to float in water.For equal mass and construction, polypropylene rope is similar in strength to polyester rope. Polypropylene costs less than most other synthetic fibers.
Polypro is a term which is generally used equally for polyester and polypropylene; depending on what is most fitting for the user’s purpose.