Merino is renowned for its warmth but what is less well known is that the Bedouin tribes of the Sinai have been wrapping themselves in wool for centuries. Merino keeps you warm when you’re cold, and cool when you’re hot.

Temperature control

Merino garments protect you from extremes of temperature because they offer superior insulation to most textiles.

Insulation due to trapped air

Since the conductivity of air is less than a tenth that of most textiles (Fig 1), the thermal insulation provided by a fabric is due not to the fibres themselves but the air trapped between the fibres. Merino is much finer than most other textiles, so, for a given weight, it contains more air spaces, and hence provides greater insulation.

Insulation proportional to thickness

Furthermore, since fabric insulation bears a direct relationship to its thickness (Fig 2), the ability to brush up the surface of Merino allows you to increase its effective thickness and hence its insulation without increasing its weight.

Protection from hot and cold

Merino’s insulation capacity has made it synonymous with warmth, yet the ability to insulate the wearer from extremes of cold also helps protect the individual from excessive heat. Like the Thermos™ that keeps hot beverages hot and cold beverages cold, Merino insulates you from the worst of the ambient temperature. This explains why Merino has been worn by both Shackleton on his Antarctic adventures and by the Bedouin of the Sinai.

Humidity control

Merino also helps maintain the micro-climate above the wearer’s skin by buffering changes in humidity.

Moisture transport

In hot climates or during strenuous exercise, the micro-climate above the skin becomes saturated with vapour, which will make the individual clammy unless their attire can absorb and release this moisture.

The ability to absorb moisture vapour expressed as a percentage of its dry weight is known as the fibre’s regain. For synthetics the regain can be as low as 1%, for cotton it’s 24%, while Merino has the highest regain with an ability to absorb 35% of its own dry weight in water. (Fig 4)

This higher regain means that Merino is better able to absorb the moisture vapour produced by the wearer and so lower the humidity in the micro-climate between the skin and the garment. (Fig 5)

CSIRO trials prove merino less clammy

In CSIRO tests, Merino transported 27% more moisture away from the body than polyester fabric of identical construction. Wearers also felt less clammy when wearing merino than wearing polyester.

Proof of temperature and humidity control

Merino's superior overall climate control was verified in a study conducted by the Ergonomics Unit at the Polytechnic Institute of Wales. The Institute compared a wool comforter with a synthetic comforter of equivalent weight and construction and the physiological data showed that the heat under the wool comforter was significantly lower 100% of the time. They also measured the humidity next to the skin and found that under the wool comforter it was lower 71% of the time.

Summary

Merino's superior insulation and its ability to absorb and release moisture mean it is better able to keep the micro-climate near the wearer’s skin at a comfortable temperature and humidity.

Sources

• Holcombe, B.V., “The thermal insulation performance of textile fabrics”, CSIRO.
• Holcombe, B.V.  “The sensational comfort of wool”, CSIRO.
• Holcombe, B.V., Staying warm”, Wild Magazine, Oct/Nov/Dec 1987.
• CSIRO, “Wool and Warmth” fact sheet
• CSIRO, “Wool garments generate warmth in cool, damp conditions”
• Stuart, I.M., Schneider, A.M., and Turner, T.R., Textile Research Journal Vol.59, pp 324-329 (June 1989)
• CSIRO, “Wool for Active Sports: Comfort and Performance Advantages”
• “The superior qualities of wool”, http://www.ecobedroom.com/1/wool_qualities.html

All figures and tables courtesy of CSIRO unless otherwise noted.