ThreadTested

Merino wool or synthetic: which base layer fits you

A base layer sits against your skin, so its fabric decides how it feels after hours of effort. The two common choices are merino wool and synthetic fabric, usually polyester. Neither wins on every point. This guide compares them on the criteria our base layer rankings use, with numbers taken from those rankings. We build scores from manufacturer specifications, independent reviews and owner reviews, and we do not test products in person.

What each fabric does well

Synthetic

Drying
Dries fast. Reviewers in the tests we read praise the synthetic tops for wicking and quick drying.
Odor
Holds smell. Reviewers in the tests we read say the synthetic tops are less odor resistant than wool.
Durability
Usually tougher, and one test says a synthetic top tolerates the dryer.
Price
Often cheaper, but not always.

Merino wool

Drying
Dries more slowly than the best synthetics in the tests we read, though the lighter weights breathe well.
Odor
Resists smell, which matters on multi-day trips.
Durability
Thin merino wears faster, and a 100% merino top needs gentle washing and drying.
Price
Cheap merino exists, but most of the expensive tops are merino.

Some merino tops add nylon to the blend. One test we read says the nylon adds durability and stretch to a wool layer.

What our ratings show

The hiking base layer rankings hold 12 long-sleeve tops: 5 synthetic and 7 merino. These are the average ratings we gave each group, on a scale of 0 to 10.

Synthetic (5 tops)Merino (7 tops)
Odor control4.28.3
Durability7.45.8
Breathability7.37.4

Merino scores far higher on odor control. Synthetic scores higher on durability. Breathability is close, so the fabric alone does not settle it: the best breathability rating in the group, a 9 out of 10, belongs to an ultralight merino top, and synthetic tops reach 8. These are our ratings of 12 tops, not lab data, and a small group can mislead. The averages show a pattern in the rankings and cannot predict every top.

How the fabric changes the score

Odor control and durability together carry 30% of a base layer score. Breathability and comfort carry the other 70%. A top that wins on fabric can still lose on the points that weigh more.

  • 45% Breathability
  • 25% Comfort and fit
  • 15% Odor control
  • 15% Durability

Which one fits you

Synthetic fits you if

  • You do short, hard efforts and wash the top after each one.
  • You want the longest life from a layer you wear often.
  • You are working to a tight budget. The cheapest synthetic and the cheapest merino in our hiking rankings both cost about $50, so check the price of the exact top.

Merino fits you if

  • You wear the same top for several days.
  • You want a softer feel against the skin.
  • You accept gentler care and a faster-wearing fabric in exchange for less odor.

Merino is the common choice at the top of the price range: 4 of the 5 tops in our Top Shelf hiking ranking are merino. The one synthetic there, the Arc'teryx Rho LT, rates 9 on durability, the highest of the group.

Base layers by sport

Running

Smart Buy, Sweet Spot and Top Shelf base layer rankings.

See running base layers

Hiking

Smart Buy, Sweet Spot and Top Shelf base layer rankings.

See hiking base layers

Cycling

Smart Buy, Sweet Spot and Top Shelf base layer rankings.

See cycling base layers

Ski

Smart Buy, Sweet Spot and Top Shelf base layer rankings.

See ski base layers

To see how we turn evidence into a rating, read how we score. For how a base layer works with the layers over it, read how to layer.