Merino Wool vs Synthetic Baselayers

By Hati Whiteley

Merino wool versus synthetic fibres? It’s certainly is a lively debate!

We asked Ronnie, our lead clothing designer, for her view on the pros and cons of using merino wool and synthetic fabrics as baselayers.

Ronnie’s response? Merino wool and synthetic baselayers both have a place in your wardrobe, to be used depending on the activity, conditions, and trip length.

Here’s Ronnie’s expert guide for when to use merino wool and synthetic base layers.

Advantages of merino wool - natures technical fabric

Next to skin comfort

To qualify as ‘merino’, the wool fibres have to be less than 24 microns in diameter. This makes merino wool some of the finest fibres found in nature. The finer the merino, the more comfortable (our Kepler range is 17.2 microns, making it officially 'ultrafine' and itch-free). For more on merino’s composition, read our What is Merino? develop.

Temperature and moisture regulation

Merino is a living fibre: it adapts to your environment. All textile fibres can absorb and desorb moisture, and merino is extremely good at it. In fact, merino wool absorbs up to 35% its weight in water, expelling it into the air to regulate your temperature. This means that stay dry and comfortable in warmer climates, and are insulated in cooler climates. The result is a garment that insulates against temperature extremes on both ends of the spectrum.

Naturally resistant to odour

By regulating moisture, merino wool reduces the growth of odour causing bacteria in the first place. Merino wool traps odour wear, releasing them only when the garment is washed. Research has also shown that merino fibres provide a less hospitable environment for odour-causing than synthetics.

Fire retardant

Merino wool is naturally flame resistant. This means that it will not melt or stick upon coming into contact with burning items.


As a natural fibre, merino wool will biodegrade under the right conditions rather than hanging around in the environment for many years.

UV protection (?)

You may have heard that merino will protect you from UVA and UVB rays. To a certain extent, this is true, however, the colour and knit of your garment can impact the protection it offers.

Advantages of synthetic


Unlike merino wool, synthetic fibres don’t absorb water. Cavities in the fabric structure wick moisture away from the skin, meaning the garment stays dry during high aerobic exertion and prevents you from overheating

Insulation and breathability

Depending on how the fabric is spun and its thickness, you’ll find synthetic base layers that prioritise breathability, insulation or moisture transport. Our Koulin range prioritises breathability and moisture-wicking, promoting a cooler feel and reducing the likelihood of overheating when you’re moving quickly.


Synthetic fabrics are usually far lighter than wool.


Synthetic fibres are more robust and hardwearing than their natural counterparts.

Kind to the skin

Fine, smooth fibres make synthetic fabrics much kinder to hypersensitive skin, and suitable for people with wool allergies.

When is merino the best base layer?

Moving slowly in variable conditions, out and about when the temperatures might drop: in these circumstances, the insulating, wicking, and cooling properties of merino make it the right fibre for the job.

Not sure whether you need your merino base layer on? Try the layering test… If you’re expecting to layer up over your base layer, you’re expecting cooler conditions so you’ll need the insulating qualities of merino.

A quick whip around the Alpkit office revealed that the AK team tend to don their merino for winter hillwalking, winter bouldering, caving, and stop-start activities in general.

When does synthetic insulation make the best base layer?

If you are going out and working hard non-stop (ish) for a while, synthetic will best meet your needs as it keeps moving moisture away from the skin and won’t get overpowered. Think cycling, warm weather hiking, trail running, fell running, and any running really… If conditions suggest you’ll mostly be wearing a single layer, go synthetic: it’s the best for keeping you cool.


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