Knowledge Base Page - The Benefits of Merino Wool

Jan 31, 2022

What is merino wool?

Merino is a type of wool that comes specifically from a merino sheep. The merino sheep breed came originally from Spain but was domesticated and bred on a commercial scale in New Zealand and Australia, with Australia still producing around 80% of the worlds merino today. The merino sheep thrives in hostile conditions where other breeds would perish, meaning that they have developed a high quality wool coat to protect from hot summers, freezing winters and everything in between. From the merino, the fine wool fibres allow these sheep huge amounts of insulation at relatively low weights and this has transferred seamlessly across into the textiles industry.


A quality merino sheep can produce up to 18kg of wool each year and the sheep do need to be shorn annually to stop the wool from growing and prevent them from suffering from heat stress, mobility issues and other health related problems. Unlike down, there is no ethical merino standard for the production and sourcing of the wool so a number of issues have been highlighted across the years but most outdoor brands are conscious of this and a number of different approaches have been taken to promote animal and ecological friendly approaches.

What are the benefits of merino fabrics?

There are a range of benefits to merino, some of which are briefly highlighted below;

Regulating body temperature – along with the high insulating values, merino is highly breathable allowing heat to be released when necessary to avoid overheating, especially during more intense activities.

Moisture control – one key difference with Merino to synthetic fabrics is Merino "holds" moisture whereas synthetics eradicate it. So Merino wool can be heavier when wet and hold up to 3 or 4 times its own weight in moisture but still keep it's natural thermo regulating properties and it is highly efficient at wicking moisture.

Prevents odour and bacteria – during activity, your body produces sweat, this develops bacteria, which is the cause of odour. The natural composition of merino with its antimicrobial design, allows sweat to sit on the surface of a product without leaving unwanted smells on the garment for a period of time. 

Skin conditions – the Merino's softness is derived from its exceptionally fine fibres, enabling them to bend far more than traditional, coarse lowland bred sheep wool fibres. This is turn has led to people with sensitive skin to feel less or no irritation when wearing a merino wool items of clothing, a huge change from traditional wool products.

How does it compare to other materials?

Merino wool is easily compared to other wool fibres as being thinner and smoother but even within this there is variation. Fibre sizes are measure the diameter of the wool fibre in microns (µm). Wool diameters can range from as much as 36-40 microns (µm) on Cotswold sheep down to around 18-24 (µm) on Merino, all compared to human hair with is around 40 (µm). However, the merino classification can be broken down further, with strong wool (23–24.5 µm), medium wool (19.6–22.9 µm), fine (18.6–19.5 µm), superfine (15–18.5 µm) and ultra fine(under 15 µm). Due to these fine fibres, much more wool (approximately 4 times more fibre per square inch) is needed to produce a garment of equivalent weight to using other conventional wools.


The reason wool was traditionally used in outdoor clothing was simple, warmth, even when wet. Wool, in general, is a high insulating material that works a similar way to down, which is created from high lofting tendril feathers from birds and fowl. The smaller fibres in merino allow air to be held in pockets. These air pockets act as a barrier and prevent loss of body heat to the surrounding cold air providing warmth and insulation perfect for use next to the skin, particularly as a baselayer.

The Figures

Much like the science behind sleeping mats in the R-value rating, there is a slightly less known scale upon which to measure thermal resistance or thermal conductance in clothing fabrics. This is known as the “Clo” which is the insulation rating value used and highlighted by some outdoor wear manufacturers. It is similar to the R-value used for sleeping mats and in direct comparison, 1 R-value (US) = 1.136 Clo (the units of thermal resistance are generally provided in m2-C/W or ft2 hr °F/BTU).


However, the unit of the Clo is slightly subjective (which may explain why it is not used as often as R-values by manufacturers) but a Clo value of 1.0 is defined as the amount of clothing needed by an inactive person to feel comfortable at a room temperature of 71F (21C). In a light breeze (having a 20 ft/min or 10 cm/sec air flow rate) with a relative humidity <50%. A value of 0 Clo would be equivalent to the amount of insulative clothing on the naked body while 4.0 Clo would be someone covered head-to-toe in windproof, highly insulating material.

To use some of this information in a more applicable way, an average cotton t-shirt would measure at around 0.8 Clo, whereas a long sleeved shirt would be around 0.25 Clo, a long sleeved merino baselayer would be around 0.34 Clo. For further context, up towards the higher end of the scale, a goose down jacket would measure at around 2.0 Clo.

How do brands use merino?

Different companies obviously use merino in different ways. Two of our biggest merino producing brands are Rab and Montane.


Rab have recently updated their MeCo range to Merino+, which blends merino wool and their new 37.5 Technology fibres. The two materials together in Merino+ baselayers offer the best of both natural and synthetic. The merino wool is able to absorb water vapour and water, regulating the body’s temperature more effectively whilst the synthetic 37.5 fabric is strong, resilient, easy to wash and dries rapidly. This combination is perfect for those undertaking high intensity outdoor activities as the new Rab Merino+ garments are able to perform at the highest standards under a wide range of conditions. Rab produces these Merino+ baselayers in two fabric weights, 120 and 160, with the Merino+ 120 more suitable for warmer conditions in spring and summer and the Merino+ 160 designed for colder winter conditions.

Montane produce a merino/PrimaLoft/polyester (a 50:25:25 ratio) blend in their trademarked Primino range. Primino combines a unique blend of high performance PrimaLoft yarns and natural merino sheep wool, creating a comfortable and ultra fast drying baselayer for year round mountain use. The PRIMINO two-weight system, Primino 140 and Primino 220, allows all round versatility so you can tailor your baselayer requirements to any condition with the same concept used again where the lower weight (Primino 140) fabric more suited to warmer conditions and the higher weight (Primino 220) more suited to colder winter conditions.

A number of brands produce merino baselayers, hats, gloves and various other items which reinforce the importance placed on merino as a high performing outdoor material.