Pool Cover Micron 250, 300,400 or 500? Which is better?

I am about to purchase a pool cover and here are a few different Micron's to choose from. Is more Micron better than less? Which is better and why? Does it affect the go together of the pool? Any other advice on purchasing a pool cover and walk unsteadily?
am looking on e-bay presently.
thanks

Answers: Their discussion about the matter thickness of the cover. The thicker the greater the cost.

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