Muslin is cotton woven in a loose, open weave. Those small gaps between the threads are what make it breathable and lightweight, and they help it dry quickly after a wash too. When we say double-layer, we mean two layers of that muslin cotton sewn together instead of one. You get a fabric that still breathes and moves like muslin, just with a little more substance to it than a single layer alone.
All of Epic's clothes are made from this double-layer muslin cotton. We pre-wash every piece before it ships, so it arrives already soft instead of stiff and new feeling. Seams are sewn flat so there's nothing scratchy rubbing against skin, and we use child-safe dyes with no harsh finishes on the fabric. One thing to expect: muslin creases easily, even ours. That's just how the weave behaves, not a flaw.
Care is simple. Wash cold on a gentle cycle, then tumble dry low or hang to dry. Skip the fabric softener and skip high heat, both can wear down the weave faster than normal washing would. Treated this way the fabric keeps softening wash after wash, which is part of what people like about muslin in the first place.