So, the idea is to place a specially shaped ballon inside of a ring around a head or cap, or in some other way. Inflating the baloon would create 360' shade around the head. It could have a part that covers the top of the head too.
Utility: many people don't have a habit of taking and using umbrellas
when it's sunny, but sunshine contributes somewhere around 80% of the aging of skin...
* Inspired by [pashute]'s "Portable Tree Shade".
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P.S. One of the mechanisms considered before, i.e., filling with small amount of H20, that turns into steam, when heated by sunshine, was dropped, mainly because of:
(i) it's inconvenient to refill it, and you couldn't collapse it quickly upon need, such as to enter a bus.
(ii) it might be hot, keeping hot steam isn't something that you'd want in a sunny day, unless there's a good thermal insulation.