**1. Introduction**

Textiles are complex porous structures, composed of fibers, yarns and fabrics. It refers to a vast and diverse application areas, and are an integral part of our lives used in many routine applications such as apparel, shoes, accessories and home furnishings. The functionality and performance of different textile products depends on their physical, mechanical, and thermal properties, as well as, air and moisture (and/or liquid) transport properties. Hence, in order to optimize and improve the performance of the textiles in diverse application areas, characterization of the textiles and an understanding of their structure–property relationships are imperative. For instance, textiles next to skin regulate the skin micro-climate, and skin-textile friction (measured by friction force or friction coefficient) play a vital role in skin comfort and health in different conditions [1]. The frictional properties of textiles can become an

important issue when it expedites the development of skin injuries. For example, excessive and repetitive friction from moist textiles (due to absorption of skin sweat) were reported to expedite tissue deformation and skin damage, friction blisters, pressure ulcers (also known as decubitus ulcers), and even more severe unwanted problems in athletes, military, and in people with compromised skin conditions and immobility [1–11]. Therefore, to optimize the fabric frictional properties, depending on applications, it is essential to have an understanding of the structural characteristics of the fibers, yarns and fabrics, and their effects on respective physical and mechanical properties in different micro-climatic conditions. These understanding can provide valuable insights on how to engineer and design textiles to lower the friction force when in contact with the skin [12, 13].

Textile characterization is also a broad topic which involves the study of polymers, fibers, yarns, and fabrics as well as their end products in diverse applications. Over the years, there has been a significant number of studies by scientists to develop theories and systematic test methods, and standardize these methods to ensure consistency in textile characterization (methods) all around the world. However, most characterization methods are destructive in nature, and/or compromise the structure during tests which may compromise the resultant data. For instance, measurement of yarn crimp% in fabrics following the ASTM D3883 (option A) test method involves the extraction of the yarns from the fabrics which may influence the measurements by releasing the tension acting on the yarns [12, 14]. In addition, natural fibers (for example, cotton) tend to be hairy on the surface. The hairiness on the fabric surfaces makes the characterization of natural fibers, yarns and fabrics more challenging. This is why there is a growing interest in nondestructive characterization of textiles. Literature reveals the use of the X-ray micro-computed tomography (XRM-CT or X-ray CT) systems for nondestructive characterization of fibers [15–17], yarns [12, 18] and fabrics [12, 19–22]. The X-ray CT system has also been well-known for nondestructive analysis and its diverse applications in biological and medical science [23], material science [24], and in the analysis of membranes [25]. The nondestructive analysis reported in these studies [12, 15–25] involved acquiring high resolution 3D images of the test samples using the X-ray CT system. CT images are reconstructed and then imported to processing software for advanced analysis of both the 2D and 3D images [12]. CT images can also be analyzed to represent different fibers with different densities using gradients of gray levels or intensities. In this chapter, a few non-destructive yarn and fabric characterization methods using the X-ray CT system and image analysis tools will be discussed. In addition, the characterized properties will be compared with those obtained from the existing classical test standards. It is to be noted that the chapter will focus on the interpretation of the test results of cotton-made yarns and fabrics.
