Today merino wool fabrics have gained a strong following amongst outdoor enthusiasts for use as next to skin base layer garments. Traditionally wool has not been used as a next to skin fabric due to its irritating abrasive qualities. Wool fibres are measured in microns, typically regular wool fibres can measure in grades of 30-40 microns with coarser wool being over 40 microns or more. However, the advent of superfine merino, primarily from the merino sheep breed, has changed this. Superfine merino wool generally consists of individual fibres at or below 18.5 microns, these superfine merino fibres are much finer and softer than regular wool and make a merino garment much more pleasant to wear directly against the skin.
The merino sheep breed was originally developed in Spain and prized for its fine wool. It was introduced to Australia in 1797 where selective breeding led to an even finer grade of merino wool being developed. Today Australian merino wool is considered to be some of the finest in the world.
Merino wool microclimate moisture management
The unusual structure of merino wool makes it a unique fibre. Unlike synthetics, which have a uniform composition both internally and externally, merino wool has a unique construction. Its outer surface is hydrophobic (repels moisture), while it’s internal structure is hydrophilic (absorbs moisture). This characteristic allows merino wool to absorb body perspiration and store it within its own structure. Merino wool can occupy up to 35% of its dry weight in moisture vapour and still feel dry to touch, this can positively influence the microclimate on your skin’s surface by locking away perspiration and reducing clamminess.
Another unique property of wool is that as it absorbs moisture internally due to its hydrophilic core, it can actually release heat through a process known as heat of sorption. This phenomenon may also explain why many report that wool feels warmer when wet compared to other fabrics. It can be considered a positive attribute in cold conditions where high energy and increased sweating rate, followed by periods of inactivity can be expected. An example of this is climbing to a high vantage, and then settling in to glass for game.
The ability of wool fibres to store moisture within their physical structure does generally make them slower drying though, particularly when compared to fibres that are totally hydrophobic, such as synthetic polyester. Water evaporates at the same rate, regardless of the textile structure it is contained within. When wetted, the hydrophilic nature of wool means it has more moisture to begin with, thus extending the drying time. It also explains why wool can become heavy when wet.
The merino fibre consists of a complex internal structure that can absorb moisture, combined with a scaly external surface that has the ability to repel water. Image by CSIRO Materials Science & Engineering Textile & Fibre Technology Program. Graphics by H.Z Roe 1992 & B. Lipson 2008, based on a drawing by R.D.B Fraser, 1972.
Merino wool odour control
One of the factors that draw many hunters to merino wool base layers over synthetic is their ability to inhibit the build-up of body odours. Sweat itself has no odour, however, if it remains on the skin for a number of hours bacteria develops that can lead to body odour. The merino wool fibre surface is not only hydrophobic but also of a scaly structure. This makes it difficult for microbes to either penetrate or attach onto the fibre surface, providing a poor environment for bacterial growth.
The very outer layer of the epicuticle also contains high concentrations of a unique C21 fatty acid bound to the surface that is linked to antimicrobial properties; while a complex internal chemistry allows it to potentially bind acidic, basic, and sulphurous odours. These are important components of body odour control.
One negative aspect of merino wool is its reputation for being less durable when compared to synthetic fabrics. This is generally more noticeable in very lightweight merino wool fabrics, with heavier materials generally fairing much better. This can generally be a factor in higher wear areas such as knees, elbows, and cuff hems. Also, areas subjected to abrasion by backpack straps and hip belts may also demonstrate signs of wear, but generally only in repeated and heavy use situations over very long periods of time.
The unique moisture management and superior odour control capabilities of merino wool make this fibre a wise choice for outdoor applications as a next to skin layer. The hunter who understands the benefits and advantages of merino wool may greatly enhance and maximise their comfort levels in the field when wearing base layers made from merino wool fabric.