This conversation occurred hours after the first round, which I drove in a vehicle without AC with internal temps reading around 113. That's the highest I've ever seen in a bus. It might actually be the top of the scale, so that it could have been even more. Later in the day, the replacement bus was a more civilized 83 degrees.
The surprising basic answer is: Actually, there are only a few days every summer when I am ready to tear it from my head because it feels like it is adding to the burden of the heat. Other than those rare times, it offers a little protection from direct sun. And I've never had a sunburned "part" in my hair since I began wearing it. Small but nice benefit. My hair stubbornly parts itself, even when firmly brushed and tied straight back. For this reason alone I will never be mistaken for a birthright Old German Baptist, since their hair always obediently flows straight back from hairline to covering edge to bun.
The more complicated answer is that the covering offers a unique line of defense against the heat. Being cotton, it absorbs and evaporates water quite effectively. So when the heat bothers me, I just whisk it off for a moment, soak it down with water from my water bottle, the hose, etc., wring it out, and put it back on. Probably no one has ever noticed that it was wet. But unless the weather is terribly humid, it makes a huge difference in helping my body keep at a functional temperature.
The passenger's follow-up comment was, "That string under the chin would drive me crazy!"
It took a little getting used to. Going through that transition in the mountains of British Columbia, where (no matter what they say) it is never too hot or too humid was a good start. I found in my first few coverings that the exact fit has a lot to do with the comfort of the strings. The little bit of elastic at the nape of the neck is a nice modern touch on my Old Order River Brethren style covering...the Old German Baptists have just a rigid binding at the back, so there's less flex in the chin strings.
Sometimes, like my OORB friends, I'll untie the strings for awhile when I'm in a semi-private setting. Some denominations never tie the strings, but leave them hanging down loose. Some have a long continuous ribbon that loops across the back of the shoulders without holding anything, or ribbons that are tied loosely at the collarbone--purely vestigial. Some cover just the back of the head, and not the ears like mine does. Most women, but especially these, rely on a straight pin at the top of the front to hold the covering firmly to the hair. It doesn't seem like it would be effective, but it is. I like the OORB style for its plain, practical work-a-day functionality. It stays on because it is tied on. And I can make them myself.
The firmly tied strings do serve a spiritual purpose, I find. Though they are not distracting, I do notice them as I move my jaw. Which means whenever I speak, there is a subtle reminder to consider my words, and be sure they are becoming to a godly woman. The slight tug of the strings reminds me that I am a light to the world that is not hidden under a bushel--when people see me, they know at a glance, from a distance, that I am a Christian. It behooves me to make sure I am comporting myself in a way that honors Christ. In this way, my every moment in the world at large is a witness to my faith in God and His son.