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Weighted Blanket Filling: Best Weighted Blanket Beads for your Body Type

Learn about different weighted blanket filling. Common blankets are filled with either plastic or glass pellets, but which is best for you?

Right now, it’s 12:48 AM, and I am researching scientific articles in order to increase the thermal conductivity of our blankets. I was thinking of postponing innovation for truHugs 2, but no…innovation must lead our way. To start with the innovation, I will take you through my process of finding the perfect weighted blanket filling.

Thermal conductivity (TC) is defined as the ability of a material to transmit heat, and it is measured in watts per square meter of surface area for a temperature gradient of 1 Kelvin per unit thickness of 1 meter. Metals and other dense solid material usually have high levels of TC, whereas less dense solids have lower levels of TC.

The higher the TC value, the cooler we can make our blanket. When you get up in the morning, the high thermal conductivity of your tiles (travertine is mostly limestone, which is even cooler to the touch than glass) makes them feel cold under your feet. Thermal conductivity can vary based on a material’s density, chemical composition, length, size, and shape.  The primary topic of this article will be on glass versus plastic weighted blanket beads, which helps lend insight into how weighted blankets are made and what’s in a weighted blanket?

Glass vs. Plastic Weighted Blanket Filling

In my search for a finding the best materials for a weighted blanket, I was searching for a weighted blanket filling that would make for a great summer cooling blanket, I first compared the two most popular weighted blanket beads in the weighted blanket industry: Polypropylene plastic pellets (PPP) and glass microspheres (GMS). First, I found an article about the thermal conductivity of polypropylene (PPP) (which is what our competitor’s plastic pellets are made out of).

According to this engineering document, the thermal conductivity of a solid slate of PPP (SSPPP) is 0.17 – 0.22 W/M K. Then I found the solid slate thermal conductivity of GMS (SSGMS) to be 1.05 W/M K. Remember, the bigger the number the cooler it will feel.

Thus, if you had two slabs of SSPPP and SSGMS (not little pellets, which is completely different because the medium then contains hundreds of little balls with air slots in between) next to each other that were each 1 meter thick, you would see the glass absorb heat 5x faster than the plastic, and it would feel cooler to touch. The data we just reviewed supports our common-sense intuition. Think about your experiences with large slabs of these materials.

Looking more specifically at glass as a weighted blanket filling, I already knew that the glass pellets used in nearly the whole concentrated weighted blanket supplier market ranged between .8 – 1.4 mm in diameter. I’m now wondering how the diameter of the individual glass microspheres that are part of SSGMS affects thermal conductivity. After some digging, I found a scientific article that shows that at 500 hPa pressure (about half normal atmospheric pressure) the glass bead size range of 0.8 – 1.4 mm all have the same thermal conductivity of .169 W/M K. There are two important trends in the table I represent just below to take note of.

First, if pressure were simulated to increase to 1000 hPa, which is what most of us are used to in our bedrooms, then the thermal conductivity would probably increase only slightly. That is, the increasing slope is not linear, but is more associated with symbols like e^ and ln. This makes sense, as we know a medium that consists of tiny little balls with air in between is probably less dense than a solid slate of material, decreasing thermal conductivity. As a very rough estimate, the thermal conductivity of the GMS is roughly 6.21x lower than the glass in the form of a slab (SSGMS).

Secondly, there is a decrease in thermal conductivity once you have a glass grain size of less than .2 mm or greater than 3.8 mm, which will make the blanket warmer, unable to release heat quickly. However, we cannot state that the decrease indifference is very great. Grain size will affect the amount of air between the pellets dependent on the radius of each pellet.

Weighted Blanket Filling of glass bead thermal conductivity values
Extracted from a material science scientific study. Shows how thermal conductivity varies based on an atmospheric pressure of where you are living and the grain size of the weighted filler.

Future Works & Update Notes

At this point, we have probably derived that if the thermal conductivity (k) decreased so much by reducing the glass density from a slab of glass, physics will accurately predict that if you take a slab of PPP and turn it into a less dense medium of air and little PPP balls, the thermal conductivity would decrease as well.

Still, even at 5x or more the thermal conductivity of plastic, I’m thinking glass may not be the ideal weighted filler, due to market analysis of weighted blankets being too hot being the second most frequent bad review critique among weighted blanket consumers during the summer. With plastic, the frequency of ‘hot’ complaints increases even more. Why is this data not referenced here? Because I know the market from looking at it for thousands of hours, and we will still formally report market trend data on our blog once our other series are more mature.

Our analysis here failed to take into consideration…. In parallel, what the TC of these two different materials is at different temperatures that match human body heat. As a notable concern, TC is directly also always dynamically dependent on the current temperature of the material. For weighted blankets, this state may change for the weighted filler as human body heat is constantly being supplied to it.

Notes for additional secondary research as this post is updated to answer questions to date:

  1. Research Polypropylene (PPP) bead industry radius mean and variance and possible epoxies that may affect TC.
  2. Obtain more accurate measure on contextual TC of PPP
  3. Compute whether the contextual TC of having temps equal to human body heat and the thickness of different layers at different sizes and weights dependent on the weighted blanket filling used. (density will have impacts)

Other Weighted Blanket Filling Options?

How about concrete? Different forms of ceramic? According to this textbook chapter on Thermal Conductivity (these are simply rough estimates to gain an idea of trends to direct our exploratory research), concrete may have thermal conductivity slightly greater than glass and may be able to be manufactured in micro pellets.

However, the manufacturing of concrete typically isn’t sustainable, causing harm to the environment. How about limestone, that’s even better than concrete. Now we have to consider maintenance and whether limestone undergoing laundry maintenance would harm the body. I will add that to my research to-do list tomorrow.

Also, we have to consider the different coatings we can apply to pellets can decrease friction and thus reduce noise during movement, and whether hollow or c-shape pellets, just like in carbon fiber, would increase thermal conductivity at a precise level we want to calculate that would be able to accommodate the North Americans populations’ metabolism heat release mean and variance for different genders.

Just maybe, TruHugs TWO design should have two different variants based on population metrics of heat release between genders.

Now it’s 1:33 AM. I will continue writing when I am feeling creative.

Is a Truhugs Weighted Blanket Right for You?

If you are skinnier, chances are you have a high metabolism and you are releasing more heat into the environment. Also if you are pre-menopausal you probably sleep hot regardless of body type.  With the plastic weighted blanket beads, you are more likely to sweat like crazy, because the low thermal conductivity values of a weighted filler made out of plastic beads are restricting the transfer of heat out of your blanket.

In order for the weighted blanket filling to transfer heat out, the weighted blanket filling needs to reach its heat capacity (HC, similar to a pot of water boiling and turning into a gas, except in this example there is no molecular state shift…there is a shift but not enough to change state…. But still a shift in TC).

In choosing the perfect weighted blanket filling, we must make sure the heat capacity provides an ambient temperature that is of comfort to the majority of the population. Plus, if we wanted to design a summer blanket variant, the perfect summer weighted blanket filling (or filler for skinny people) would be able to have a material that has lower HC with bead size that maximizes TC.

In our grand opening in February, we will host a huge social media vote on what industry flaws our potential customers want to be fixed or increase in quality material construction at specific price estimates for TruHugs TWO. At that time, tell us what you want from our list of possible innovations, and we will make it a reality. Your will, our hands.

Our recommendations on Weighted Blanket Beads 

Please, you will be most convinced if you allow 10 minutes to research which blanket you should buy. We encourage you to Google the different materials you are comparing with the following scientific words and submit resources to us in terms of how you made your decision, even if you buy a competitor’s blanket. Our idealism of information, completeness, and thoroughness can only be accomplished with your help. Large contributors will be offered a chance to win a free truHugs TWO blanket along with a $500 spa coupon. Look for our grand opening in February for more information.

Research-Informed Weighted Blanket Filling Suggestions

For textile thermal regulation factors: a) thermal breathability, b) thermal absorptivity, and c) weighted filler thermal conductivity… higher values typically represent a trend of coolness.

Great blanket characteristics if you are skinny, sleep hot:

a) textile fabrics with high thermal breathability and absorptivity

b) weighted blanket filling with high thermal conductivity and lower heat capacities.

Who you should buy from – US, our design quality maxes breathability over other bamboo blanket manufacturers. In doubt? We encourage you to examine the effect of cotton thread count and single-ply construction on breathability and durability. In addition, research the difference between viscose, modal, and lyocell…all different variants of bamboo fabric that vary in their mechanical properties.

Great blankets if you have a slower metabolism, sleep cold:

a) textile fabrics with minimal breathability, but maximum absorptivity to keep a “heat sack” next to your body as you sleep.

b) weighted filler with low thermal conductivity (to serve as a wall that is an obstacle to heat escaping to the environment in the first place) and higher heat capacity. (to increase the size of your heat sack)

Who you should buy from, our friends @ Sensacalm, Gravity, The Magic Weighted Blanket.

That’s right, we are so honest we will even point you towards the competition.  Can’t we all get along like Tellytubbies? We hope our time invested in sharing information from our R & D process (counter-intuitive I know, we will just have to innovate every order as everyone starts imitating us) helps you make the best-weighted blanket purchase decision.


When my brother started truHugs, I was skeptical as to whether weighted blankets really worked. Using my research background in Kinesiology I quickly dove into the science to discover that weighted blankets, to my surprise, have some documented positive effects during use. Obsessed with product improvement, I promise to use my background in a diverse field of sciences to continually help improve our products for maximum comfort and benefit. I hold a M.S. in Kinesiology and M.B.A. along with 13 industry related certifications.

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