Muslin is cotton woven in a loose, open weave, not a synthetic material, and that weave is what makes it breathable and quick to dry. People often ask whether muslin is really cotton or some kind of synthetic, and the answer is plain cotton, just woven more loosely than a typical onesie fabric. It softens with every wash. It also creases easily, which is normal for a loose weave, not a flaw.
Synthetic baby clothing, things like polyester fleece or acrylic blends, is made from petroleum-based fibers. Those trap heat and moisture against the skin instead of letting air move through. Cotton is a plant fiber instead, and an open weave like muslin's lets even more air through than a tighter weave does, which is part of why muslin breathes better than regular cotton. Plant fiber versus plastic fiber is a simple, real difference you can judge for yourself.
Epic's pieces are double-layer muslin cotton, pre-washed so they arrive soft instead of stiff. They're sewn with flat seams and finished with child-safe dyes, with no harsh finishes added. Wash cold on a gentle cycle and skip the fabric softener, then tumble dry low or hang, since high heat isn't kind to cotton. Sizes run roughly newborn to 4 years, and if you're still weighing muslin against a tighter cotton weave, this side-by-side on muslin and regular cotton lays out the practical differences. Epic is Vanessa and Bob's small family business, designing in Bali. They ship worldwide with tracked delivery and take unworn returns within 30 days.