Same way. Synthetic bags don't hold up nearly as well as down to repeated or prolonged compression, so store them uncompressed. I think we worry more about down, because a high quality down bag is so expensive.

For either type, fluffing up in the dryer (low heat) to remove any dampness is a good idea before putting them away.
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey