When it's really hot
Recently I have been confronted with an environment that made me explore quite an opposite direction in functional apparel, from my dominant one. For years I was putting all of my attention into how to keep one warm and dry. And suddenly I had to look to the opposite side of spectrum, on keeping one cool and protected from sun. The only connecting aspect in those two fields is that you need to deal with perspiration. Which actually allowed me to test one idea that I was having for rain jackets ventilation, but on a summer dress.
We were planning to go on a road trip in Arizona and Utah in May, so the first destination was Phoenix and it was forecasted that it would be around 30-33 degrees C and coming from San Francisco, where summer does not exist, I didn’t have any adequate summer clothing.
So, as always happens to me couple of weeks before a trip, I started feverishly designing new pieces.
I started with the question of what is adequate type of clothing for hot, sunny, medium to low humid conditions:
- It should be loose to allow for uninterrupted convection, which is the most efficient way for body to cool down (we sweat, it evaporates from the surface of skin, water needs energy to change states from liquid to vapor, so it takes your bodily heat to do so, thus cooling you);
- It should provide adequate protection from sun for two reasons. One is protection of the skin from ultraviolet, that is harmful if overdone. Second one is to protect from heat radiated by sun: less heat absorbed by body surface - less heat to get rid of. All this factors led to necessity of covering as much body surface as possible, while keeping it far from body surface and to the need of careful choice of fabric (regarding composition and color);
The points above can be broken down to smaller ones, but since it was my first, crude approach to design a clothing for a hot weather I wouldn’t go into it.
What solutions I came up with:
Loose A-silhouette knee-long dress, with loose long sleeves. Generous armpit vents. Front and back upper openings. Experimental vertical vents on front and back. High collar on the back. I chose a very thin, not densely woven cotton, black one. Now you would say that black objects heat up faster than objects of any other color, and I can’t argue with that, at the same time black absorbs most of the radiation from the sun, including UV, so that it lets the least amount of it to pass through fabrics.
How those features worked:
Overall silhouette worked fine, long wide sleeves allowed for full coverage or arms, while you could easily rolled them up, without restricting the airflow (as would be the case with sleeves that narrow down towards cuff). The front and back openings on the top center allowed hot rising air to escape *if it would be a loose garment with a tight collar, the air would stay trapped, preventing efficient convection*.
The hot air rises, that led me to think about ways for it to escape. I began with wide neck opening, but this alone would not be enough, the hottest areas of the body are the center chest and a region along center back, widest between shoulder blades. So I devised vertical vents right next to that areas, but not just mere openings, I wanted them to have higher volume of airflow, so I made them three dimensional, a row of half pipes, reinforced to keep shape.
The generous armpit openings worked out the best on this dress, they provided real good ventilation.
Field testing of a dress revealed some flaws:
The vertical vents on the back get easily flattened and blocked with a backpack. However the backpack in the hot environment is not the best way to carry things, I think it’s almost impossible to keep the back substantially ventilated while wearing backpack, any backpack cut the air flow inside the garment, trapping it in the hottest region, along the center back. So there should be alternative bag options for hot climate.
Another little flaw was that once it get a bit chilly all this ventilation areas become areas that cold air easily crept in from. So either the garment should have a closure for them, or it needs to be used only in stably hot environments. I was testing it in Grand Canyon for example, there are areas where cold air accumulates and flows from small canyons upwards, or it could be pretty cool in the shaded areas. However this dress as a hiking backup worked just great.
I started my descend dressed a bit warmer, but after 30 minutes I was so hot, I changed to this dress (which due to its fabric weight is very light and compact) and went all the way back up wearing it and it was a great protection from sun and it ventilated real well.
That’s how I started the hike:
That’s how I have returned:
Unfortunately during the rest of the trip in high altitude deserts weather was way colder, which I had not expected, and I had to wear all the clothes that I have to keep warm, I even bought beanie and gloves on the way, so I couldn’t test the dress more.