There is a strong relationship between textile materials and its quality. Quality of textile materials is manifested in different ways such as aesthetic appeal, feel or hand, etc. It is basically judged by how a textile material feels when touched or handled. It is also judged by the comfort experienced. What does comfort mean? The term comfort is described as "the lack of unpleasantness" according to some experts. Comfort is a condition or feeling of pleasurable ease, well-being, and contentment. There is general acceptance that the transfer of heat and water vapor through a garment are possibly the most significant factors in clothing comfort.
According to a recent study, thermal equilibrium is the most significant and the only one standard of comfort. It is clear that the state of comfort can only be attained when the most complicated interactions between a range of physiological, psychological, neurophysiological and physical factors have taken place in a satisfactory manner. Through combination of impulses passed through the nerves from a variety of peripheral receptors like visual, auditory, smell, taste and touch in the brain, the comfort is realized. Amongst them, clothing comfort is mainly connected with skin sensory systems.
The clothing comfort can be segregated further into three groups.
1. Psychological comfort
2. Tactile comfort
3. Thermal comfort
Psychological comfort
It is mostly related with the visual appeal which covers size, fit, color, luster, style, fashion compatibility etc.
Tactile comfort
Tactile comfort is related to fabric surface and mechanical properties.
Thermal comfort
Thermal comfort is connected to the ability of fabric to maintain the temperature of skin during transfers of heat and perspiration generated within the human body. There are two aspects of wearing a comfort of clothing:
. Thermo-physiological wear comfort which involves the heat and moisture transfer characteristics of clothing and the manner that clothing facilitates to maintain the balance of heat of the body during various activity and movement.
. Skin sensational wear comfort which is connected with the mechanical contact between the fabric and the skin, its smoothness and flexibility in movement and its lack of prickle, irritation and sticking when damp.
Clothing comfort
Now comfort is considered as a primary aspect when a textile product is valued. The comfort characteristics of fabrics mostly depend on its structure, kind of raw material used, weight, moisture absorption, heat transmission and skin perception. Clothing comfort can be classified under two broad sections:
- Sensorial comfort
- Non-sensorial comfort.
Sensorial comfort
Sensorial comfort is an experience 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. The brain then processed these sensory signals to formulate subjective perception of sensations as follows:
Tactile sensations: scratchy, itchy, picky, static, prickly, tickling, rough, raggy
Moisture sensations: sultry, nonabsorbent, clingy, clammy, damp, wet, sticky
Pressure (body fit) sensations: heavy, soft, stiff, snug, loose, lightweight
Thermal sensations: warm, hot, cold, chill, cool
These sensations are suitable largely in summer wear, sportswear and body-fit garments.
Sensorial properties are all about the performance of a fabric on skin contact, and depend on the fibre material used, the construction of fabric (surface structure) and the treatments of fabric finishing. 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 area of contact 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.
Non-sensorial comfort
Non-sensorial comfort basically related 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 covers 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 ^ A^ (Tsk - Tab)
Evaporative heat loss: He = ke ^ A ^ (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 vapor pressure of water at skin temperature, Pab = ambient vapor pressure (*covers not only the still air layer close to the body but also the thermal properties of the clothing worn.)
Characteristics signifying to clothing comfort
Fabric hand
A fabric hand or handle describes the way a fabric feels when it is touched by human hand and gives an idea 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 described. Heller discussed the differences between active and passive touch and he differentiated 'synthetic touch' with 'analytic touch'.
Katz classified 'active touch' into four categories:
. Gliding touch,
. Sweeping touch,
. Grasping touch and
. Kinematics grasping touch.
Texture, which is another factor of hand, 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 many 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 vital part to play in maintaining the 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 single clothing system is suitable for all occasions and climates. A clothing system which is suitable for one climate may not be suitable for another climate. Good thermal insulation properties are required for clothing and textiles used specially in cold climates. The thermal insulation properties depend on number of factors like thickness and number of layers, drape, fibre 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 entire 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 noted that thermal resistance to transfer of heat from the body to the surrounding air is the sum of three parameters:
-the thermal resistance to transmission of heat from the surface of the material,
- the thermal resistance of the clothing material, and
- the thermal resistance of the air interlayer.
It is clear that heat transfer through a fabric is a complex phenomenon affected by lot of factors. The three major factors in normal fabrics appear to be thickness, enclosed still air and external air movement. Out of all these, the entrapped air is the most important 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 also have a major contribution towards thermal comfort in the end.
Air permeability
Air permeability describes the characteristic of fabric to allow air to pass through. The air permeability should be as low as possible in outdoor clothing because it should act as a wind protection. The air permeability of a fabric can be said is a measure of how well it allows the passage of air through it. The passage of air is important for a number of fabrics depending on the end uses such as industrial filters, tents, sailcloths, parachutes, raincoat materials, shirtings, downproof fabrics and airbags. Basically, the air permeability of a fabric can influence its comfort behaviours in number of ways. In the first case, a material that is permeable to air is in general, likely to be permeable to water as well, 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 depends on the enclosed still air inside, 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 which are to be worn during vigorous activity. The human body cools itself by sweat production and evaporation during periods of vigorous activity. For instance, the clothing should 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, then the moisture is captured between skin and clothing and heat is accumulated in the body. As a consequence, heat and moisture starts building up, causing discomfort, wet skin and skin abrasion.
Water repellency and water absorption
The surface tension properties of fibre or fabric are changed by water repellency treatment as that they repel water drops. Treated fabrics are not completely impermeable to water. The treatment also improves soil repellency to some extent. Water resistance is required 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.
For diapers, liquid water transmission is an important feature. It is the ability to absorb and capture liquid inside the fibers and not letting it escape. If sweat condenses to liquid it must be able to be transmitted away from the skin surface for the comfort. 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, which 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 for the desired comfort, a process that is encouraged by absorption within a body-covering. Both mechanisms are needed simultaneously for the desired comfort though both the 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
So far it can be said that comfort of apparels has not been objectively expressed, although it can be recognised through experiences 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 two most important comfort criteria in the apparel of twenty first 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 depending on the end use of the apparel by appropriate finishing treatments to the fabric. As the evaluation of comfort depends on the handling of fabrics which is a frictional phenomenon, lot of research and studies are currently carrying out on the surface properties of fibers, yarns and fabrics.
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