"Only YOU can prevent forest fires." Smokey the Bear (pipe smoker, I mean why wouldn't he be!?)
A cap is/was important, not to protect the smoke or the smoker, but to control ash and embers from setting the world on fire.
(Not to be confused with a discussion of Esoterica tobacco blends.)
So. Somewhat on the opposite end of the spectrum from smoking your pipe in the inverted mode, smoking with a cap on your pipe has its origins outside, not inside.
http://pipesmagazine.com/forums/topic/why-do-some-smoke-the-pipe-upsidedown
The history of wind caps and elegantly-capped smoking pipes extends back to outdoorsman -- amateur and professional.
My colleagues and friends who work in the desert southwest of North America -- the Sonoran and Mojave biomes of AZ, CA and Sonora MX -- have a hard and fast rule about the use of smoking pipe caps. The old guys out there would confront any young park ranger or field biologist whose pipe didn't have a wind screen or cap. Whether the pipe was lit, full, cold, empty, no matter. "Where's the cap." Never a question, but an interrogative. No cap/screen? Your pipe stays in the office today.
Law enforcement pipe smokers would note and confront tourists about whether they knew about the dangers their pipe smoking posed to the great natural beauty they were visiting, too.
One of the first and greatest collection of capped smoking pipes I ever saw was possessed by a park ranger at a national monument in the southwest US. His family and friends gifted this guy with wind screens and capped pipes from all over the world. His retirement gift, instead of a watch, was a top of the line capped Peterson.
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