Tailorability refers to the ease with which a fabric can be fashioned to create a garment, and includes factors such as sewability, drape, setting, shape-retention, and wrinkle-resistance. Merino is popular with the world’s bespoke tailors and catwalk designers because it is considered to be one of the most tailorable of all textiles.

Sewability

Merino has several advantages for tailors and dressmakers, whether they are professional or amateur. It cuts cleanly, doesn’t fray, won't crush when handled, and pins don’t mark it.

Drape

Drape refers to the manner in which a fabric hangs or falls. Merino is renowned for its excellent drape, which is due in part to the natural elasticity of the fibre. Cotton, by comparison, which doesn’t have the same elasticity, is considered to have a particularly poor drape.

Setting

Setting is one of the methods tailors use to shape fabric, and is an area in which Merino enjoys an advantage over other fabrics. Whereas synthetics are set by heat, Merino can be set and shaped by either chemicals or high temperature steam and pressure. This flexibility means Merino can be finished in a number of ways to produce different effects.

Steam pressing

Merino can be readily formed by steam pressing, and on cooling the shape of the fabric is retained. This simple process enables garment-makers to produce flat seams, sharp creases and complex structures such as shoulders in jackets without puckering. Steam pressing or a warm iron can also easily remove wrinkles formed during wear.

Cohesive/temporary set

The shape that is formed in Merino by steam pressing is usually referred to as “cohesive” or “temporary” set as it can be readily removed by further pressing or by allowing the fabric to relax in water. Both water and temperature are required to set a Merino fabric. The lower the moisture content or “regain” of the fabric the higher the temperature required. Since Merino has a very high regain (Fig 1), it can be set at a lower temperature than most fabrics.

Glass transition temperature

The relationship between regain and the temperature required for setting is known as the “glass transition temperature” (Fig 2). Above the glass transition temperature, Merino displays rubber- or plastic-like properties and it can be readily shaped and set, but below the curve it is stiffer and more difficult to deform. In scientific terms, below the curve, Merino behaves as a “glassy” material.

More control with Merino

A similar phenomenon also occurs in synthetic fibres and other amorphous materials. However, most synthetic fibres absorb much less moisture than Merino, and the glass transition can only be exceeded by the use of heat. In addition, for Merino, the glass transition only occurs in the water sensitive ‘matrix’ regions of the fibre, and the water insensitive ‘filaments are unaffected. Again, this allows a high degree of control in achieving desired outcomes.

Forming creases

Forming a crease or shape in the rubber region and cooling into the glassy region while holding the shape will set the fabric, and this shape will be retained until the glass transition temperature is again exceeded. This set can be achieved by steaming followed by cooling (red arrow in Fig 2), or by wetting and drying the fabric at the same temperature (green arrow in Fig 2). Cohesive setting by steaming is also used to remove twist liveliness of Merino yarns or to thermally splice a Merino yarn.

Why ironing requires water

An analysis of the glass transition diagram (Fig 2) also indicates why it is difficult to iron a crease out of a Merino garment if no steam is used. Using a hot iron, the fabric dries out and the glass transition temperature cannot be exceeded unless an extremely high temperature is used. With an increase in regain from a spray of water or shot of steam, the glass transition temperature is exceeded and wrinkles can be readily removed or creases inserted.

Relaxation shrinkage

Relaxation shrinkage may also be introduced into a garment or fabric by overstretching and cohesive setting the new stretched dimensions. This shape will be retained until the fabric becomes wet or is steamed. Once this happens, the fabric or garment will shrink back to its relaxed dimensions. A small amount of relaxation shrinkage is desirable in woven fabrics as it aids in the moulding of garment shape during manufacturing. However, excessive relaxation shrinkage may lead to garment sizing and garment deformation problems.

Summary

Merino is a favourite of tailors because of its sewability, renowned drape and its unique ability to be set under a wide variety of conditions to produce an infinite variety of effects.

Sources:

• Leader, John, D. (1984)  Merino - nature’s wonder fibre, Ocean Grove, Vic.: Australasian Textiles Publishers,
• Morton, W.E. and Hearle, J.W.S., [1993] Physical Properties of Textile Fibres, 3rd Ed., Manchester, UK.: The Textile Institute.
• Rippon, John et al, (2003) Merino, in Encyclopedia of Polymer Science and Technology, New York : Interscience Publishers.

All figures and tables courtesy of CSIRO unless otherwise noted.