Chapter 20 Thermal Insulation and Porosity—From Macro- to Nanoscale Dana Křemenáková, Jiří Militký, Mohanapriya Venkataraman and Rajesh Mishra Abstract Porosity of textiles is one of the main factors influencing their thermal conductivity and insulation. Porosity in textile fabrics is the combination of fiber porosity, yarn packing density, and voids due to fabric construction. It is shown that assemblies from very fine fibers tend to suppress radiation and convection heat transfers because of huge total surface area, which restricts the free flow of air passing through them. For effective thermal insulation especially at low tempera- tures, it should be selected sufficiently high thickness of textile layer as well. Porosity is therefore decisive parameter for the evaluation of thermal comfort expressed in special units “clo.” The main aim of this chapter is the prediction of the effect of porosity of fabrics and fibers on the thermal conductivity and insula- tion. The changes of thermal comfort due to the use of hollow fibers and multilayer corrugated nonwovens are described. The thermal properties of highly porous aerogel structures are discussed. Enhancement of insulation by their inclusion into textiles is investigated as well. 20.1 Introduction Volume porosity is defined as the ratio of free space volume occupied within a material to the total volume of the material. Nonporous material is one that has a porosity of less than 0.25 and a porous material having usually a porosity greater than 0.4 [1]. Depending on the nature of the pores, three types of pores can be D. Křemenáková (&)  J. Militký  M. Venkataraman  R. Mishra Department of Material Engineering, Faculty of Textile Engineering, Technical University of Liberec, Studentská 2, 461 17 Liberec, Czech Republic e-mail: dana.kremenakova@tul.cz M. Venkataraman Department of Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India © Springer International Publishing Switzerland 2017 J. Šesták et al. (eds.), Thermal Physics and Thermal Analysis, Hot Topics in Thermal Analysis and Calorimetry 11, DOI 10.1007/978-3-319-45899-1_20 425