How do I look after merino wool base layers?
Merino base layers resist odour genuinely, so they need washing far less often than synthetics. What kills them is heat, biological detergent and rucksack abrasion — not dirt.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 3 min
Short answer
Air a merino base layer overnight rather than washing it after every wear; it genuinely does not develop the odour a synthetic does. When you do wash it, use 30 degrees, a wool or non-bio detergent, a low spin, and air dry. Never use fabric conditioner, never tumble dry, and expect wear holes at the shoulders and waistband where a rucksack or a belt rubs, because fine merino is a light fabric doing a hard job.
Merino base layers cost a lot and get worn out fast by people treating them like sports polyester. The care is different in both directions: they need washing much less often, and the washing they get needs to be much gentler.
Step by step
- Air it instead of washing it.Turn it inside out and hang it somewhere with moving air overnight. Wool holds moisture inside the fibre rather than on the surface, and the surface chemistry does not support the bacteria that make synthetics smell, so a merino layer is genuinely wearable again the next day.
- Wash at 30 degrees on a wool or delicate cycle.Turn it inside out first so the abrasion falls on the inside face. A mesh bag helps if the load contains anything with a zip or a hook.
- Use a wool wash or a plain non-bio detergent.Biological detergent digests protein, and merino is protein. This is the single most common way people ruin an expensive base layer without noticing until it thins.
- Skip the fabric conditioner entirely.Conditioner coats the fibre, which destroys the moisture management that is the whole point of the garment, and it leaves a residue that then holds odour.
- Spin low and dry flat or on a line.A hard spin creases and stresses fine knit. Never tumble dry even superwash merino: the heat shrinks it and hardens the handle.
- Accept and manage the abrasion points.Fine merino is 150 to 200 grams per square metre of very fine fibre. Rucksack straps, belt lines, seatbelts and bra bands wear it through. Rotating two garments, and putting a lightweight layer over the top under a pack, doubles the life.
- Repair holes early.A small hole in a knit grows every wear. Darn it or use an iron-on knit mending patch on the reverse as soon as you see it.
Tips
- Merino blended with a little nylon — commonly around 12 to 20 per cent — is markedly more durable than pure merino at the same weight, at some cost in feel and odour resistance. For a base layer under a pack, that trade is usually worth taking.
- Weight tells you the use: around 150 gsm for summer and running, 200 gsm as an all-round base layer, 250 gsm and up for cold and static conditions.
- If a merino layer does eventually smell, a soak in a wool-safe wash with a little white vinegar in the rinse shifts it. It is a much rarer event than with polyester.
- Moths eat merino base layers in storage just as readily as they eat a jumper. Wash before storing at the end of the season.
Common mistakes
- Washing merino after every single wear out of habit — Every wash is mechanical wear on a fine knit. Airing preserves the garment and works, which is not true of polyester.
- Washing merino in the same load as towels or jeans — Heavy items abrade fine knit in the drum. Wash base layers with other lightweight items.
- Assuming machine washable means dryer safe — It almost never does on wool. The dryer is where merino base layers shrink and go hard.
Questions people ask
Why does merino not smell when polyester does?
Two reasons. Wool absorbs moisture into the fibre core rather than leaving it on the surface, so odour-forming bacteria have less free water; and wool binds odour compounds within the fibre rather than releasing them. Polyester is the opposite on both counts.
How many wears before it needs washing?
Several days of ordinary wear, or a couple of days of hard exercise. Judge it by feel — wool tells you honestly when it is done.
Why has my merino base layer developed holes at the shoulders?
Rucksack strap abrasion, almost always. It is not a moth if the holes are exactly under the straps and the edges look worn rather than chewed.
Can I put merino in a 40 degree wash?
Occasionally, on a superwash merino, without disaster. But 30 with a wool detergent is what makes the garment last, and there is no cleaning benefit at 40 that a proper detergent dose does not deliver.