"Bloom" — before and after.
I spotted my new Hunter rubber boots in the closet the other day, and they looked like they were covered in mildew. I was bummed; I'd chosen these boots because they have a matte finish and I figured they wouldn't "bloom" as much as the glossy ones do. I've heard that the bloom is caused by temperature changes. Whatever the cause, it looks awful. The Hunter website says:
Occasionally, you may notice a white powdery "bloom" on your Hunter rubber footwear, this is because rubber is a natural product and in certain conditions, insoluble particles may rise to the surface. This is a normal process, characteristic of high quality, natural rubber and nothing to be concerned about.
This process does not affect the performance or durability of your boots. A pristine finish and shine is easily restored with regular use of Hunter Boot Buffer, or Instant Boot Shine, available from good Hunter retailers, as well as from our online store
From what I've seen, it doesn't happen "occasionally." It happens a lot, whether you wear your boots or not. Perhaps it gets better with time.
I don't have any of Hunter's anti-bloom products, so I used olive oil and paper towels to get rid of the bloom. It's easy: just apply some oil, rub off the excess, and buff until the surface feels dry. You can see the result on the first boot, above. I wonder how long it will last.