Most... if not all?... Self-Inflating Mats should be stored with inlet valve open, so effectively inflated, or at least part inflated.
Rolled up in a bag is technically for transporting only, not for long/medium term storage.
That's assuming this one has internal foam, and it's also assuming you care about manufacturers instructions. Some folk ignore such instructions... usually due to lack of storage space at home. No idea how that plays out long term, as we store our Exped SIM's inflated.
Probably check out the actual storage instructions for this particular model, before making a decision?
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