Comfort related testing .1 Introduction

The Permetest was used in this study for measuring the comfort related properties of all of the fabrics. The literature review examined various pieces of equipment utilised for testing comfort related properties of fabrics. Even though thermal and sweating manikins are modern and advanced pieces of equipment, and probably the preferred method for testing comfort of garments and ensembles, the Permetest has the ability to test both the water vapour permeability and thermal resistance of fabrics, and is fairly widely used for research. According to Gericke and Van der Pol (2010), the debate regarding whether sweating manikins, or the Permetest and Alambeta are the most representative of actual wearing conditions, is an ongoing one. It is important to note that measurements on sweating manikins are carried out over a 10 hour period, whereas measurements on the Permetest are completed within a very short period, usually 3 minutes. Research conducted by Gericke and Van der Pol (2010) on three knitted fabrics made from different fibres, tested on Walter the sweating manikin, the Permetest, and the Alambeta, showed that the three test methods exhibited the same trends. It would therefore be expected that, if the commercial suiting fabrics used in this study, were tested on a sweating manikin, similar trends would be observed as those found with the Permetest. This can be the topic for further research.

3.2.2.2 Permetest

The Permetest, at the Department of Polymer Science at the University of Stellenbosch, was used to test the fabrics for three comfort related properties, namely water vapour permeability, water vapour resistance and thermal resistance.

These three comfort related properties represent the dependent variables of this study.

99 Before testing commenced, samples were conditioned for 24 hours in a laboratory at a temperature of 21ºC (±2°C) and 65% (±2%) humidity.

Three measurements were taken per fabric (also used by Oğlakcioğlu and Marmarali, 2007). One measurement consisted of 5 repeats, each on a different fabric specimen. The average, standard deviation and coefficient of variation were determined for each set of measurements.

3.2.2.3 Testing procedure for water vapour permeability and resistance Before testing the water vapour permeability and resistance of the fabrics, the water reservoir of the Permetest was filled with water, and the wind speed was set to 1m/s. The procedure that was followed for determining the relative water vapour permeability and water vapour resistance on the Permetest was according to the guidelines provided in the instrument testing manual (Hes, 2009). Under isothermal conditions, relative water vapour permeability and resistance were determined as follows:

Calibration procedure:

1. Without a sample on the Permetest, press Reference Start on the computer and wait until steady state is achieved.

2. Insert blue calibration sample, press Sample Start on computer, wait until steady state is achieved.

3. Repeat until the water vapour resistance value lies between 4.8 and 5.2. If not, then press Calibrate on the computer and repeat steps 1 and 2, until a value between 4.8 and 5.2 is obtained.

Test procedure:

1. Without a sample on the Permetest, press Reference Start on the computer and wait until steady state is achieved.

2. Place sample on the measuring head of the Permetest, press Sample Start on the computer and wait until steady state is achieved.

3. Write down the values for relative water vapour permeability and water vapour resistance.

100 4. Repeat steps 1 to 3 five times on different samples each time

5. Refill the water reservoir of the Permetest regularly.

As discussed previously in the literature review, the relative water vapour permeability refers to the ability of a fabric to transport water vapour to the external environment; whereas, water vapour resistance is the resistance that a fabric has against the transmission of water vapour. The water vapour permeability of a fabric is particularly important in clothing, because if a garment is unable to transmit moisture vapour when the body perspires, the perspiration will not evaporate from the skin surface and can even wet the garment, resulting in severe discomfort.

Therefore, Mehta (1984) and Kothari (2006) recommend that, in order for a garment to be classified ‘breathable’, and to transmit perspiration vapour, the water vapour resistance of the fabric should be as low as possible, and the water vapour permeability should be as high as possible.

3.2.2.4 Testing procedure for thermal resistance

Before testing the thermal resistance of the fabrics, the temperature gradient was set to 10°C and the wind speed was set to 2 m/s. The procedure followed in order to test the thermal resistance was according to the guidelines provided in the instrument testing manual (Hes, 2009). The procedure was as follows:

Calibration procedure:

1. Deselect Isothermal Mode on the computer.

2. Without a sample on the Permetest, press Reference Start on the computer and wait until steady state is achieved.

3. Insert the black calibration sample, press Sample Start on the computer and wait until steady state is achieved.

4. Repeat until the thermal resistance value equals 59. If not, press Calibrate on the computer and repeat steps 3 and 4, until a value of 59 is obtained.

Test procedure:

1. Without a sample on the Permetest, press Reference Start on the computer and wait until steady state is achieved.

101 2. Place sample on the measuring head of the Permetest, press Sample Start

and wait until steady state is achieved.

3. Write down the value for thermal resistance.

4. Repeat steps 1 to 3 five times on different samples each time.

Thermal resistance, which refers to the resistance a fabric provides against the movement of heat, is significant in terms of the comfort related properties of fabrics due to it determining thermal comfort. The literature review identified that the thermal insulation that a fabric provides depends, to a large extent, on the thickness of the particular textile and the volume of air that is provided for the entrapment of air. Other external factors influencing thermal resistance is the design of garments, whether the design includes openings that will increase air movement, and as a result reducing thermal resistance.