Wool vs. Synthetic fleece blanket test – Insulation face off

For those who haven’t seen the YouTube video or read my previous posts on the subject I am attempting to build a natural fabrics based setup for wild camping in UK upland areas. This differs slightly from classical bushcraft setups, where natural fabric based kit is popular, as bushcraft settings allow us to supplement carried kit with fires and natural insulation, e.g. piled vegetation under bedding for insulation. Additionally as I will be carrying all of this kit on long mountain walks it needs to be suitably lightweight for performance required.

Now obviously synthetic fabrics are simply lighter in most cases so this is as much about gaining first hand practical experience of the real performance difference in the field, as well a pushing the possibilities with some slightly different design ideas.

My initial sleep system choices for differing conditions is documented in another post, building a sleep system for all seasons, so I won’t repeat that but a key component of all seasonal and temperature options is of course at least one insulation layer. The simplest, most easily sourced insulation layer for any sleep system being a trusty blanket. Probably the most commonly used blanket for wild camping being army surplus variants, typically wool, which meets my natural fibre project objectives. So the army syle wool blanket is my reference point for designed a natural fibre insulation layer

Army wool blankets are versatile, tough and reliable, but heavy. My UK version weighs in at 1.8kg and certainly would not provide a comfortable night at zero degrees (C) whereas a much lighter sleeping bag can certainly achieve this.

Reading the forums, opinions differ wildly on just how warm wool blankets are. Some swear by them, others not so much. I want to bit more hard evidence of really how effective they are in a measurable sense. A natural first comparison point being versus that outdoor staple standard fleece (with an added bonus that relevance goes beyond blankets to mid layers in clothing etc.)

The testing approach

Whilst anecdotal experience is great and most videos assessing warmth of different sleeping options rely on it, I wanted a more controlled scientific approach. i.e. something that would help me understand how comfortable I would be by layering additional insulation elements into a system.

A start point for this being to understand just how warm the wool blanket is versus other blanket types. This could also then inform others. e.g. if someone is slightly too cold at 8 deg C in a wool blanket how much difference would a sleeping bag liner make.

And hopefully initially lead me to answer a key question: are wool blankets warmer than fleece ones??

My test uses some basic household equipment and a “repeat” a few times approach to validate results. The core principle is to use a fixed amount of heated water in a plastic cup and calculate the loss of energy with different insulation layers.

Equipment

• 3 X identical plastic cups
• Measuring jug
• Infra red thermometer to measure surface temperature
• Insulation materials to test
• Timer
• 3 X clothes pegs to cinch insulation materials together in as similar a way as possible.
• 3 X identical plastic lids

Method

1. Enclose each cup with selected insulation method taking care to get an even wrap. One is left bare as a control.
2. I tested in my conservatory as there is no breeze and a fairly constant temperature which helps isolate to pure insulation testing.
3. Fill each cup with 200ml of heated water (I used hot water from the tap)
4. Take initial surface temp reading.
5. Take readings every 5 minutes for half an hour and one after the hour.
6. Convert change in temperature to kJ energy lost to give a quantitive measure of energy loss that would negate slight variances in start temperatures etc.

Test 1. Wool versus synthetic fleece blankets

I tested two blanket types initially. A mid thickness type fleece (test 1a) and subsequently a thick piled fleece (test 1b) versus the military surplus wool blanket. Notably the standard fleece weighed in around 25ogsm (grams per square metre). The army surplus blanket around 550 gsm and the thick piled fleece around 510gsm.

Blanket Type	Weight (gsm)	Energy Loss (kJ)
None (control)	–	15.3
Army wool blanket	550	12.04
Black Fleece blanket	25o	12.96
Test 1b.
None (control)	–	13.7
Army wool blanket	550	10.45
Thick pile fleece	510	9.2

(Note: the difference in relative performance versus the control betweem 1a and 1b are due to slightly different room temperatures and time between first and last readings.)

Conclusions – Is wool or synthetic fleece warmer?

No great suprises here but the answer is “it depends”. The quality and weave type of both types of blankets plays a part but there a few takeouts I am happy to stretch to.

1. The army surplus blanket was a better insulator than the similar thickness but lighter weight black fleece blanket. it maintained about 8% more heat energy
2. When we upped the fleece to the thick pile version of similar weight to the wool we saw the synthetic outperform the wool. It lost about 12% less heat.
3. Insulation is about stopping heat transfer, and the loft i.e. air trapped as insulation and thermal conductivity of the fibres will both play a part. Wools thermal conductivity is 0.04 W/mK. Thermal conductivity for polyester about 0.05 W/mK (results of quick google so happy to be corrected). So inherently the polyester probably conducts slightly more heat as a material, but this is secondary, and the lofting characteristics are the most important element.
4. So if you want to stay warm with a blanket and there is no wind or fire to contend with look for the one with the best loft (fluffiest), and likely synthetic will provide more bang for buck or weight. If you want pure versatility and to withstand a bit more wind and possibly a campfire wool is still the way to go.

What next?

Irregardless of the fact that in pure insulation terms the effectiveness is more about the weave and loft than the material, my project is to create a natural fibre system. My feeling is that the relatively low loft of the army blanket, i.e. dense weave gives it some great additional qualities, fire resistance, wind and water resistance for bushcraft, but compromises pure insulation. As I am build my system for wild camping with no fire, and using a tarp and oil skin (waxed canvas) bivvy bag, I think a much fluffier wool blanket will provide better insulation, and also a liner and layering (air pocket) effects that creates would also be beneficial.

So I aim to test both the additional insulation provided by liner and also some alternative blanket types in coming weeks. For ultimate loft though am considering creating a down quilt, possible in combination with raw sheeps fleece, to supercharge that warmth.