Tactile aspects of clothing comfort
4.1 Tactile comfort sensations .1 Human tactile responses
Tactile aspects of clothing comfort
4.1 Tactile comfort sensations 4.1.1 Human tactile responses
The tactile sensation of clothing is very important for clothing comfort.
Tactile comfort of clothing is based on the human sensory response to clothing materials and is sensed by a variety of thermal, physiological and mechanical stimuli [1, 2]. During wearing of clothing, the clothing materials make contacts with the skin where numerous receptors are located which give rise to various sensations felt by the wearer. Touch and tactile properties are very important parameters to be considered for fabrics that come into direct contact with the human skin. On wearing clothing, the tactile sensations are mainly produced when clothing contacts and impacts local skin of human body [3, 4]. The tactile parameters of all these fabrics affect the clothing comfort, because the sensory feel of clothing materials is dependent on the mechanical stimuli due to pressure and frictional forces [2, 5]. When the clothing materials come into contact with the human skin they stimulate the various mechanoreceptors (e.g. free nerve endings, root hair plexus, Merkel’s discs, Meissner’s corpuscles, Pacinian corpuscles and Ruffini corpusles) present in the different layers of skin (i.e. epidermis, dermis and subcutaneous zone). The face, the torso and the hand are the most tactile sensitive skin areas of human body [6].
The textile fabrics are the thin sheet materials and the typical tactile characteristics of textile materials are the flexibility, compressibility, surface texture, extensibility, friction, etc. The surface and bulk properties of textile fabrics are one of the most frequently used tactile characteristics of fabrics. Fabric softness is a complex tactile sensation which determines the initial tactile perception of a wearer towards the clothing even before the wearing of the clothing. The fabric softness is commonly perceived by pressing or squeezing with fingers. The softness or fullness sensations of fabrics are objectively expressed by compressibility and resilience characteristics. The fabric frictional characteristics influence the tactile
sensations of clothing to a great extent. The Merkel’s discs and the Ruffini endings play are mainly responsible for tactile sensations related to surface texture and touch of fabric [7, 8]. Due to their location, receptive field and response type, the Pacinian, the Merkel and the Meissner mechanoreceptors can characterize the roughness of fabrics, whereas the Ruffini and Meissner mechanoreceptors can characterize the friction between skin and fabric [9]. The causes of the prickle from the skin contact of fabric can be detected by the pain receptors [10].
4.1.2 Tactile characteristics of clothing
The low stress mechanical properties of fabrics (e.g., bending, shear, extension) are objectively measured to assess the tactile characteristics of fabrics. Kawabata Evaluation Systems for Fabrics (KES-F) and FAST (Fabrics Analysis by Simple Tests) systems are available for measuring the fabric handle related characteristics. But, as far as the tactile responses are concerned, all the low stress mechanical characteristics directly or indirectly stimulate the touch, pressure, roughness and other mechanoreceptors of human skin.
The prickle sensation due to clothing is one of the most irritating discomfort sensations for clothing wear next to skin. A special type of pain nerve is responsible for prickle sensation. Individual protruding fibre ends from a fabric surface are responsible for triggering the pain nerve endings, when contacting the skin. Perceptions of prickle sensations require combined responses from a group of pain nerves.
Fabric prickliness can be measured by using low pressure compression testing, laser counting of protruding fibres and a modified audio pick-up method [11]. Matsudaira et al. [11] modified Kawabata compression tester (KESF-3) to measure the relationship between applied pressure and fabric thickness at the initial stage of fabric compression, i.e. when bending of fibres protruding from fabric surface takes place during compression. WRONZ developed laser hairiness meter where the fibres protruding from the fabric surface are counted by laser beam. This gives fairly good indication of prickliness of fabric. The sensitivity of the instrument was found inadequate for the detection of all the fabric surface hairs, where the coarser and stiffer hairs are preferentially detected [2]. Matsudaira et al. [11] also used a modified audio pick-up technique (Fig. 4.1) for measuring the mean force per contact with the protruding fibre. They have observed that this technique is the most effective measure of fabric prickle and the result obtained from this instrument correlated well with the subjective perception of fabric prickle.
Itchiness is also found to result from activation of some superficial pain receptors. The perception of itchiness in clothing is highly correlated with perception of prickliness and both the sensations are considered as important tactile sensory components [12, 13]. The sensation of fabric itchiness depends on the fibre diameter, fabric thickness at low and high pressures, and fabric surface roughness [2].
The frictional interaction between fabric and skin during contact are the key factors determining some of the important tactile sensations, i.e.
perceptions of roughness, smoothness and scratchiness. Presence of moisture at the skin surface alters the intensity of fabric roughness perceptions due to change in friction. As moisture content increases the friction between skin and fabric surface increases, which results in displacement of skin and thus more and more touch receptors are stimulated. This is the reason for a fabric that is perceived to be comfortable when a person is not sweating may be perceived to be uncomfortable under sweating conditions [2].
Mehrtens and McAlister [14] reported that the scratchiness was the greatest source of discomfort and in terms of scratchiness and clinginess men are slightly more critical than women, which is due to the fact that generally men perspire more than women. They have developed an objective method to test the scratchiness of fabrics in which a fabric was passed over a microphone yielded a scratchiness sound. In that method, the fabric was moved at the speed of 7 yd/min across a brass sheet above a microphone and the signal from microphone was then sent through an integrating amplifier into a recorder. They have observed good correlation between subjective sensation and objectively measured values of fabric scratchiness, as shown in Fig. 4.3.
4.3 Subjecting and objective scratchiness ratings [14].