What primary physical drawback occurred to the early Macintosh coats when exposed to summer heat?

Answer

The material could become sticky

Because the waterproofing relied on natural rubber treated with a solvent, the finished coats suffered from limitations; specifically, in the summer heat, the material could become sticky and unpleasant to the touch.

What primary physical drawback occurred to the early Macintosh coats when exposed to summer heat?
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