How to Evaluate a Palm Cooling Device
Palm cooling is an effective technique for improving performance and accelerating recovery. Its applications in sports are plentiful: increase your training volume, gain strength faster, and reduce fatigue during competitions.
Palm cooling works by boosting the body’s natural ability to offload heat. When we exert effort and generate heat, localized blood flow in our palms, soles of our feet, and cheeks can be up to 10X greater than other skin regions. By cooling our palms, we can reduce our core body temperature and allow ourselves to push harder longer.
However, to get the benefits of palm cooling, there are several important parameters that must be respected. We designed the Narwhals to meet these parameters for effective palm cooling in a portable, easy-to-use, and cost effective device. You can also use this checklist to evaluate other devices or guide your own DIY solution.
Temperature Control
A palm cooling device should maintain a temperature of 50-60°F (10-15°C). This is where you maximize the cooling effect. Above this threshold, the cooling effect is tempered. Below this threshold, your palms will vasoconstrict, limiting blood flow, and prevent the offloading of heat.
There are differences between individuals and circumstances. Some people can handle lower temperatures without vasoconstricting, especially if they are very hot. However, for most people in most conditions, you can’t just hold onto some ice.
Ideally, a palm cooling device must provide a mechanism for whisking away heat. If you plunge your hands in cool water, you will develop a thermal barrier around your palms preventing the heat exchange.
So cool water could work, but you need to continuously move your hands. Of course, soaking wet hands and a source of cool water are not particularly convenient for most activities. Many devices, including our first prototype, use some kind of recirculating cool water source.
The Narwhals transfer heat using heat pipes (more on this next) and achieve the ideal temperature control via our Cool-not-Cold™ packs which have a higher melting point than ice. This means that the heat you offload into the device goes towards melting the pack, versus heating up the water. The result is that the handles maintain a surface temperature of ~55°F (13°C).
Temperature Control
If you want all the gains from palm cooling, it’s important to understand thermal conductivity. To wrap your head around it, try this simple experiment.
Open your refrigerator and touch a few different surfaces: the plastic inner walls, a glass jar, and an aluminum can. Everything in your fridge is the same temperature, but some objects feel much colder. Why is that?
Even though these objects are the same temperature, the faster heat flows from your hand into the object, the colder it feels. The primary factor in this fridge experiment is the thermal conductivity.
Thermal conductivity is the rate that heat is transmitted through a material when a temperature gradient exists. It’s measured in watts per meter-Kelvin and is often referred to as the K value.
Different materials have different K values. For a palm cooling device, you want to use materials with high thermal conductivity, aka a high K value.
Among the worst:
- Glass: 1.2
- Water: 0.59
- PVC (plastic): 0.2
- Air: 0.03
Among the best are:
- Diamonds: 2200
- Silver: 429
- Copper: 386
- Aluminum (6061): 167
For the Narwhals, we use copper heat pipes, which is a technology used in space-craft and computers to regulate temperature without moving parts. We chose heat pipes as the handle for our palm cooling device because they have 100X the thermal conductivity of copper due to their innovative design.
Heat pipes are an evacuated tube containing a tiny amount of working fluid and a wicking structure on the inner walls. When a warm object, like your palm, contacts the pipe, the fluid evaporates, quickly moves down the pipe as vapor, drops its heat as it condenses, and then wicks up the walls to repeat the cycle.
This system forms an effective heat pump, which achieves an extraordinary level of thermal conductivity and prevents the creation of that dreaded thermal barrier mentioned earlier.
Usage Duration & Portability
Think about your training conditions. Do you have an air conditioned gym with a cool water source (and don’t mind refilling a device)? Or are you in a hot garage gym? Or do you play your sport outside and need something that will last hours regardless of the ambient temperature?
There are three questions to ask here:
- How long can the device last without being charged or refilled?
- How much cooling power does it have?
- Will the device fit into my training or game?
Our first prototype consisted of copper pipes with a recirculating water source. It wasn’t portable, but it worked in our home gyms. However, we wanted something that would go everywhere we wanted to train.
If you want a simple DIY solution, you could get a high quality aluminum water bottle and fill it with cool water. This setup will have good thermal conductivity, but you would need to agitate the bottle while holding it to avoid thermal barriers. You also need to refill the bottle frequently. And it will warm up very quickly in warm conditions. If that works for you, great!
Our palm cooling device is made of a double-wall vacuum sealed thermal reservoir that preserves the coolness for 2-5 hours depending on conditions.
The Narwhals also have no moving parts nor do they need to be charged thanks to those fantastic heat pipes! In terms of set up, you add the Cool-not-Cold packs and fill with 60-65°F (16-18°C) water. After about 10 minutes, the handles will be ~55°F (13°C).
Lastly, each Narwhal measures 11 inches (27.9 cm) tall and 4 inches (10.2 cm) wide. It weighs 3.2 lbs (1.45 kg) when filled. They easily go from the weight room to the sidelines!
Checklist for Evaluating a Palm Cooling Device
Before buying or building a palm cooling device, consider science and usability.
In short, does it:
- Maintain the correct temperature for palm cooling
- Provide effective heat flow for efficiently offloading heat
- Have a mechanism to prevent thermal barrier formation
- Enable enough cooling power to cover your workout or game
- Allow for easy access at the gym and during competitions
If you have questions about palm cooling or the Narwhals, reach out on Instagram, Twitter, LinkedIn or say hi@apexcoollabs.com!
