Bandanas seem to be magical in what they do. In reality, it's just pure, simple science. The better this process is understood, the more benefit can be derived from the bandana's use. Also, disappointments will decrease, knowing exactly what a bandana can and can't do.
3 natural elements interact with each other and determine the bandana's performance: temperature, relative humidity and air velocity (wind).
Temperature - since bandanas depend on evaporation for their cooling effect, and evaporation depends on heat, then the hotter it is, the higher the bandana’s evaporation rate.
Putting a bandana in the fridge, gives an exaggerated feeling of coolness, but evaporation will not start until the bandana warms up again. This results in a perception that the bandana is not cool enough. It is important to remember that a bandana can only produce a lower temperature than the ambient (surrounding) air.
In a recent test, we soaked 39 different bandana models and hung them up in a large unventilated room. After 48 hours, we tested the bandanas for temperature difference. The room temperature was 74.5 F and the bandanas were 6.5 – 7.7 degrees cooler than ambient with an average difference of 7.2 F.
Then we opened 2 large windows in the room and returned 12 hours later to perform the same test. The ambient temperature was 80.8 F, the bandanas were 8.4 – 10.0 degrees cooler than ambient with an average difference of 9.4 F. These measurements are fairly typical, with performance declining slightly over time.
All temperature measurements were taken with a non-contact infra-red temperature sensor with digital readout.
Physically and psychologically, this temperature difference is important in helping you feel cooler. In particular, the carotid artery, which is located at the front of your neck, on both sides, will sense the coolness and transmit this information to the brain.
Too often, people tend to just drape the bandana around their neck, not getting the maximum benefit of “feeling” cool. It is best to wear the bandana snugly by tying a loose knot, so that the bandana is in contact with the neck over its full circumference.
Relative Humidity – the air’s ability to hold water vapour. The higher the temperature, the more water the air is able to hold. High humidity is usually associated with high temperatures, even though the relative humidity may be the same. 60% RH at 70 F (21 C) is a lot more comfortable than 60% RH at 90 F (32 C), simply because the air can hold more water at higher temperatures.
Try this experiment. On a day when you are wearing your bandana, and you feel comfortable, walk in to an air conditioned building. As you enter the building, it should feel like someone has just put a bag of ice around your neck. The main purpose of central air conditioning is to remove humidity from the air while keeping the air temperature roughly the same. When you enter the building which contains drier air, your bandana”s evaporation rate rises, and you feel cooler.
Air Velocity – how much air is moving around, most often caused by wind.
If you are relatively motionless, for example reading a book or sun tanning, the air surrounding your neck/bandana will absorb water from the bandana’s evaporation, and gradually absorb less as the air reaches water vapour saturation for its temperature at that moment. If you are moving (walking, jogging cycling, etc) then the air surrounding your neck will be constantly changing for drier air and the evaporation rate will increase. The faster the air around your neck changes, the cooler the bandana will feel. In fact, the most common complaint from cyclists is that the bandana is too cold!
If you work in a hot, non air conditioned space, having a fan blow air at you will significantly increase your comfort.
In summary,
1 - The higher the temperature, the better the bandana works.
2 - High humidity levels will decrease the cooling effect.
3 - Under all conditions, more air moving around the bandana will increase cooling.
4 - For continuous use, it is best to soak a bandana for a minute or two at the start of your day.