The question comes up in almost every order conversation, usually accompanied by some anxiety about doing the wrong thing. People have heard that wool itches, or that cotton pills, or that one is somehow more "natural" than the other. Most of what floats around online on this topic is written by shops selling yarn, so the framing is predictably optimistic about whichever fibre they happen to stock.
Here's a more practical version, based on what we've seen actually happen to pieces after two winters and fifteen washes.
The case for merino
Fine merino — specifically 18.5 micron or finer — is soft enough that most babies don't react to it at all. The "wool is itchy" association comes from coarser sheep breeds used in commercial yarns. Merino is different in fibre diameter and that difference is the one that actually matters against skin.
The practical advantages are real. Merino regulates temperature better than cotton because the fibre structure traps air. A merino hat keeps a baby comfortable across a wider temperature range than an equivalent cotton one, which matters in Dutch weather where you go from a warm car to a cold street in thirty seconds. It also has natural antimicrobial properties, which means it can be worn more than once before washing. This matters for pieces that are awkward to wash frequently — overalls, for example.
The limitation is washing. Merino needs to be treated carefully — hand wash or a wool cycle at 30°C. Even "machine washable" merino will felt eventually if you're not consistent. For parents who are already managing laundry on four hours of sleep, this is not a trivial consideration.
The case for cotton
Organic cotton is simpler. It goes in the machine at 40°C, dries quickly, and is almost impossible to ruin. For parents who want to actually use a piece rather than worry about it, cotton has a real argument.
Cotton breathes differently than merino. It absorbs moisture rather than wicking it, which makes it better in warm weather and worse in cold. A cotton hat in a Dutch January doesn't really do the job unless it's layered. But for a spring piece — a lightweight romper for a baby who's going to spend time in a warm room — cotton is the right call.
Organic cotton specifically is worth the premium if you're knitting something for newborn skin. Conventional cotton is one of the more pesticide-heavy crops; that residue doesn't entirely wash out. Whether it matters at the quantities in a single garment is debatable, but when the choice is available and the price difference is modest, organic is reasonable.
What we actually recommend
For winter hats, always merino. The warmth difference is obvious and for a hat, one hand wash per week is not a hardship.
For overalls and rompers worn daily, the merino-cotton blend is the most practical. It handles like cotton (machine washable, dries fast) while keeping some of merino's warmth and softness. Most of what we make in the 3-18 month range uses this blend.
For summer pieces or any situation where someone tells us the baby has had skin reactions before, organic cotton. Always.
The one thing worth ignoring entirely is the label on the pattern. Commercial knitting patterns are written to be knitted in whatever yarn the designer was sponsored by. "Recommended yarn" is marketing, not a technical specification. The actual question is fibre diameter, processing and washing instructions. We're happy to go through this with you in the order conversation.