Comfort characteristics of apparels

The term comfort is defined as “the absence of unpleasantness or discomfort “or” a neutral state compared to the more active state of pleasure”. There is general agreement that the movement of heat and water vapour through a garment are probably the most important factors in clothing comfort, says Dr Subrata Das

In a recent literature survey, thermal equilibrium is identified as the most important single criterion of comfort. It is obvious that the state of comfort can only be achieved when the most complex interactions between a range of physiological, psychological, neurophysiological and physical factors have taken place in a satisfactory manner. Comfort is perceived by integration of impulses passed through the nerves from a variety of peripheral receptors like visual, auditory, smell, taste and touch in the brain. Out of which, clothing comfort is basically associated with skin sensory systems. According to a literature, the clothing comfort can be divided into three groups i.e. psychological, tactile and thermal comfort. Psychological comfort is mainly related to the aesthetic appeal which includes size, fit, colour, luster, style, fashion compatibility etc.

Tactile comfort has a relationship with fabric surface and mechanical properties. Thermal comfort is related to the ability of fabric to maintain the temperature of skin through transfer of heat and perspiration generated within the human body. Saville reported two aspects of wear comfort of clothing; (i) thermophysiological wear comfort which concerns the heat and moisture transport properties of clothing and the way that clothing helps to maintain the heat balance of the body during various levels of activity and (ii) skin sensational wear comfort which is based on the mechanical contact of the fabric with the skin, it is softness and pliability in movement and its lack of prickle, irritation and cling when damp.

Clothing comfort

Today comfort is considered as a fundamental property when a textile product is valued. The comfort characteristics of fabrics mainly depend on the structure, types of raw material used, weight, moisture absorption, heat transmission and skin perception. Basically, clothing comfort can be categorised under two broad components viz. sensorial comfort and non-sensorial comfort.

Sensorial comfort

Sensorial comfort is a perception of clothing comfort which is sensory responses of nerves ending to external stimuli including thermal, pressure, pain etc producing neurophysiological impulses which are sent to the brain. These signals are responded suitably by adjusting the blood flow, sweating rate or heat production by shivering. These sensory signals are processed by the brain to formulate subjective perception of sensations which are clustered as follows:

i. Tactile sensations : prickly, tickling, rough, raggy, scratchy, itchy, picky, staticky

ii. Moisture sensations : clammy, damp, wet, sticky, sultry, nonabsorbent, clingy

iii. Pressure (body fit) sensations : snug, loose, lightweight, heavy, soft, stiff

iv. Thermal sensations: cold, chill, cool, warm, hot.

These sensations are applicable mainly in summer wear, sportswear and body-fit garments.

Sensorial properties describe the performance of a fabric on skin contact, and depend on the fibre material, the fabric construction (surface structure) and the fabric finishing treatments. The hand properties are a very complex concept including dimensional changes at small forces (tensile, shear, compression and bending), surface properties (friction and roughness) and surface coolness or warmness. A smooth fabric surface has a large contact area with the skin and thus it may feel cool to skin because a thermal insulative air layer is absent. Surface friction affects not only hand properties but also safety in use.

Low friction suggests a slippery material, which although may improve its drapeability will decrease its safety.

Non-sensorial comfort

Non-sensorial comfort basically deals with physical processes which generate the stimuli like heat transfer by conduction, convection and radiation, moisture transfer by diffusion, sorption, wicking and evaporation.

It also includes mechanical interactions in the form of pressure, friction and dynamic irregular contact. Non-sensorial comfort is not only comprised of thermal and moisture transmission but also includes air permeability, water repellency and water resistance. The heat and moisture transfer behaviour of clothing has been studied intensively by Fourt and Hollies and Hollies and Goldman. They have used various equations to describe heat and moisture transfer in clothing which are as follows:

Convective heat loss :

Hc = kc ˆ Aˆ(Tsk - Tab)

Evaporative heat loss :

He = ke ˆ A ˆ (Psk - Pab)

Where,

kc = coefficient for convective heat transfer*

A = surface area of the body

Tsk= mean weighted skin temperature of the surface of the body

Tab = dry bulb temperature

ke = evaporative coefficient, determined by Lewis relationship (ke = 2.2 kc)

Psk = saturated vapour pressure of water at skin temperature

Pab = ambient vapour pressure

*involves not only the still air layer around the body but also the thermal characteristics of the clothing worn.

Properties contributing to clothing comfort

Fabric hand

A fabric hand or handle depicts the way a fabric feels when it is touched by human hand and gives an indication of texture of the fabric. This property is a subjective sensory complex sensation obtained by active manipulation of neural sagaciousness of our hands. Our hands perceive the fabric texture using sensory mechanisms like muscle sense and kinesthesia. The mechano receptors in the glabrous skin of our hands, equipped with large number of nerve endings having about 17,000 units that are sensitive to non-noxious mechanical deformation play a key role in subjective assessment of the fabric handle. Different types of ‘touch’ in differentiating the ‘fabric handle’ between wearing a garment and handling a fabric have been reported in the literature. Heller discussed the differences between active and passive touch and he distinguished ‘synthetic touch’ with ‘analytic touch’. Katz classified ‘active touch’ into four categories:

(i) Gliding touch,

(ii) Sweeping touch,

(iii) Grasping touch and

(iv) Kinematic grasping touch.

Another factor of hand is the texture, which is the uniformity and variation of the surface that describes it’s actual or implied features. Texture is a sensory perception that covers various aspects of surface features of the fabrics including visual, auditory and tactile perceptions and can be described in ways such as smooth, rough, shiny or dull. Among them, roughness is an important aspect which has been studied extensively and reported to have difference in perception between touching with the fingers and feeling by the skin during the wear.

Thermal comfort

Clothing has a large part to play in the maintenance of heat balance as it modifies the heat loss from the skin surface under the same time has the secondary effect of altering the moisture loss from the skin. However, no one clothing system is suitable for all occasions. A clothing system which is suitable for one climate may not be suitable for another climate. Good thermal insulation properties are needed in clothing and textiles used in cold climates. The thermal insulation depends on number of factors namely thickness and number of layers, drape, fiber density, flexibility of layers and adequacy of closures. The thermal insulation value of clothing when it is worn is not just dependent on the insulation value of each individual garment but on the whole outfit as the air gaps between the layers of clothing can add considerably to the total thermal insulation value. This assumes that the gaps are not so large that air movement can take pace within them, leading to heat loss by convection. Because of this limitation the closeness of fit of a garment has a great influence on its insulation value as well as the fabric from which it is constructed. The resistance that a fabric offers to the movement of heat through it is of critical importance to its thermal comfort. In studying the thermal insulation properties of garments during wear, it is reported that thermal resistance to transfer of heat from the body to the surrounding air is the sum of three parameters:

(i) the thermal resistance to transfer heat from the surface of the material,

(ii) the thermal resistance of the clothing material, and

(iii) the thermal resistance of the air interlayer.

It is obvious that heat transfer through a fabric is a complex phenomenon affected by many factors. The three major factors in normal fabrics appear to be thickness, enclosed still air and external air movement. Out of which, the entrapped air is the most significant factor in determining thermal insulation. There are “microlayers” (those between contacting surfaces of the materials) and “macrolayers” (between non-contacting surfaces) of air enclosed within an assembly, and an increase of either of these can increase thermal insulation. However, the characteristics of fibre, yarns, fabrics and garment assemblies have also a major contribution towards thermal comfort.

Air permeability

Air permeability describes the property of fabric to let through air. In outdoor clothing it is important that air permeability is as low as possible because it should function as a wind protection. The air permeability of a fabric is a measure of how well it allows the passage of air through it. The ease or otherwise of passage of air is of importance for a number of fabric end uses such as industrial filters, tents, sailcloths, parachutes, raincoat materials, shirtings, downproof fabrics and airbags. Generally, the air permeability of a fabric can influence its comfort behaviours in several ways. In the first case, a material that is permeable to air is in general, likely to be permeable to water, in either the vapour or the liquid phase. Thus, the moisture-vapour permeability and the liquid-moisture transmission are normally closed related to air permeability. In the second case, the thermal resistance of a fabric is strongly dependent on the enclosed still air, and this factor is in turn influenced by the fabric structure.

Water vapour transmission

The water vapour permeability of fabrics is an important property for those used in clothing systems intended to be worn during vigorous activity. The human body cools itself by sweat production and evaporation during periods of high activity. For instance, the clothing must be able to remove this moisture in order to maintain comfort and reduce the degradation of thermal insulation caused by moisture build-up in cold environment. Water vapour transmission is essential in determining the breathability of clothing and textiles in outdoor wear as well as in indoor wear. A breathable textile allows extra heat loss by evaporation of moisture through the clothing layers. If clothing layers are impermeable the moisture is captured between skin and clothing and heat is accumulated in the body. As a consequence, heat and moisture is building up, causing discomfort, wet skin and skin abrasion.

Water repellency and water absorption

Water repellency treatment modifies the surface tension properties of fibre or fabric so that they repel water drops. Treated fabrics are not absolutely impermeable to water. The treatment may also improve soil repellency. Water resistance is needed in outdoor clothing for protection against rain and is requirement for furniture and bed covering to protect against liquid excretions. Textile and clothing can be water repellency treated with finishing agents or they can be made totally water resistant with coating or laminated membranes. Liquid water transmission is an important feature of diapers. It is the ability to absorb and capture liquid inside the fibers but not letting it escape. If sweat condenses to liquid it must be able to be transmitted away from the skin surface. In considering the movement of liquid, water through a fabric, two comfort aspects may be identified. Water from an external source, e.g. rain, should be prevented from reaching the body, an aim that is achieved by using a water-resistant barrier. On the other hand, water generated at the body surface as perspiration should be removed as quickly and as efficiently as possible if comfort is desired, a process that is encouraged by absorption within a body-covering. Both mechanisms are generally needed simultaneously although two requirements are diametrically opposite. Some textile end uses such as towels, cleaning cloths, diapers and incontinence pads require the material to absorb water. There are two facets to the absorption of water: one is the total amount that can be absorbed regardless of time and the other is the speed of uptake of the water. These two properties are not necessarily related as fabrics of similar structures but with different rates of uptake may ultimately hold similar amounts of water if enough time is allowed for them to reach equilibrium.

Conclusion

Comfort of apparels has not been objectively expressed so for, although it can be recognised through experience of a person. Comfort is purely a subjective criterion. However, it can be quantified in an objective manner in terms of the properties of non-sensorial comfort characteristics. Satisfactory thermal equilibrium and efficient moisture management are the most important comfort criteria in the apparel of 21st century. Both the sensorial and non-sensorial fabric comfort depends on various factors including the type of the material, method of construction of textile substrate, feeling of the wearer, impacts due to climatic condition of the environment and its variation. Comfort can also be imparted according to the end use of the apparel by appropriate finishing treatments to the fabric.

(The author is Manager, Consumer Testing Services (Laboratory), SGS India, Bangalore)