Test method Transient thermal response of textile fabrics made of natural and regenerated cellulose fibers Sanja S. Pavlovi  c a , Sne  zana B. Stankovi  c b, * , Du  san M. Popovi  c c , Goran B. Popari  c c a Belgrade Polytechnic, Brankova 17, 11000 Belgrade, Serbia b University of Belgrade, Faculty of Technology and Metallurgy, Textile Engineering Department, Karnegijeva 4,11120 Belgrade, Serbia c University of Belgrade, Faculty of Physics, Studentski trg 12, P.O. Box 368,11000 Belgrade, Serbia article info Article history: Received 12 November 2013 Accepted 18 December 2013 Keywords: Textiles Cellulose fibers Thermal diffusivity Thermal absorptivity Specific heat abstract The thermal parameters that describe the transient response of cellulose textile fabrics due to the changes in physiological and environmental conditions were analyzed. Starting from the specific heat of the knitted fabrics determined by a new experimental method based on Newton’s cooling rate law, and previously determined thermal conductivity of the knits, their thermal diffusivity and thermal effusivity (absorptivity) have been determined. Ac- cording to the results obtained, it can be concluded that the structure of the knitted fabrics is responsible for their transient thermal response through thermal conductivity, whereas the composition of the knits influences their dynamic thermal behavior through specific heat. Hemp based textile fabrics are proved to be at a comparable level to other cellulose fabrics from the viewpoint of thermal behavior during the dynamic stage of heat transport. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Beyond a protective function, clothing constitutes a dynamic system managing the hygro-thermal exchanges between the human body and environment. Since textile materials are essentially a mixture of fibers, air and mois- ture, each having distinctively different thermal charac- teristics, their thermal behavior is the collective and interactive results of these constituents. The heat transfer mechanisms in porous textiles include conduction by the fiber polymer, conduction by intervening air, radiation and convection, but the conduction of heat by fibers is consid- ered to be the most important. In steady-state conditions when the temperature gradient driving the conduction is constant, the temperature field (after an equilibration time) in the material does not change any further. In other words, the amount of heat entering the material is equal to amount of heat coming out. The param- eters describing the thermal behavior of textile material under steady-state conditions are thermal conductivity and thermal resistance. Before the steady-state heat flow is reached, and during any period in which temperatures are changing in time, a non-isothermal dynamic stage of trans- port exists. In this transient heat transfer through textile fabric, the conduction of heat also makes the most important contribution. Non-steady state situations appear after an imposed change in temperature at a boundary of the mate- rial, or with temperature changes inside the material as a result of a new source of heat suddenly introduced within the material. These non-steady state situations occur when the skin temperature or ambient temperature rises changing the temperature at a boundary of the fabric. Dynamic circum- stances inside the fabric may occur at high physical activity level. When a clothed man sweats during activity (or due to change in ambient temperature and humidity) the sweat accumulation develops within the fabric because of condensation or absorption by fibers. The absorption, desorption, condensation and evaporation of sweat involves * Corresponding author. Tel.: þ381 11 33 03 857; fax: þ380 11 33 70 387. E-mail address: stankovic@tmf.bg.ac.rs (S.B. Stankovi c). Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymertesting.2013.12.010 Polymer Testing 34 (2014) 97–102