A good set of ear plugs should reduce noise to about 85db, which will still allow you to hear what you need to hear. In fact the HSE (yes, I know we all hate them!) recommend that too much reduction in sound is a bad thing, like you say you still need to be in touch with the environment. If you want to bore yourself silly there's some good info here...

http://www.soundadvice.info/thewholestory/san5.htm

Foam ones are fine, but I'd suggest you try a few types out to see what suits best, everyone will give you a different opinion, and everyones ears are a different shape. I'd always go for ones with a BS EN 352.2/2002 mark, because they'll have been tested and WILL do what they say/claim (many aren't though).

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