## 1 Introduction  
In the last decade, an increasing all-society interest in green materials, technologies, and services can be witnessed--partly due to natural resources exploitation, partly due to the constantly growing human liability to natural wealth and expanding consciousness of climate change. A significant amount of research is being carried out to help replace raw chemicals coming from oil feedstock with renewable ones, following the aim to cut down the carbon footprint and ecological human imprint on the environment. These chemical agents and their consequently derived compounds are often sourced from biological commodities, coming from industrial plants production [1]. As a consequence of the emerging technologies and sustainability implementation in technology practice, there has been considerable interest in agro-waste sourced from the industrial crops plantation, especially from oily-seeds plants that are a raw material for bio-diesel synthesis [2]. So far, animal feeds, soil fertilizers, and pellets to be incinerated for heat energy production are the main fields of application of the crop-stalks agro-waste, even though botanical fibers are praised for their low density, specific mechanical properties, biodegradability, low carbon footprint, renewability and affordability [3]. Likewise, there have been considerable traditions over generations in using fibers from plant sources in various applications, especially in textiles and affordable housing construction, straw reinforced mud bricks [4], rammed earth [5] and reed roofs [6] being examples. A considerable amount of energy launched by the civilized cultures serves, apart from being used as a source in transportation, as heating facilities in constructions (almost 1/3 to 1/2 of the contribution to CO\({}_{2}\) emissions) [7]. Not only within the operation, but during the procedure of manufacturing, while installing and throughout the final demolition, the energy embodied in the building materials represents the total energy consumption of a building [8]. Low density, high specific heat capacity and low thermal conductivity represented by a coefficient of \(<\) 0.1 W m\({}^{-1}\) K\({}^{-1}\) is demanded from a material to qualify as a building thermal insulation [9]. So far, wooden products [10], bamboo [11], straw bales [12], and other industrial crops like, for example: sunflower [13], corn cobs [14], hemp [15] and cotton stalks [16], or less common fibers like Ichu [17] have served as a heat building insulation in structures. Straw bales are perhaps the most explored naturally available and sustainable thermal insulation and construction material. Their thermal conductivity was reviewed during experimental measurements as a function of density and straw-fiber orientation towards the heat flow. Direction specified, perpendicular thermal conductivity was 0.045-0.056 W m\({}^{-1}\) K\({}^{-1}\); then, in a parallel direction, it was 0.056-0.08 W m\({}^{-1}\) K\({}^{-1}\), showing increasing values depending on the density of a straw bale [18]. Furthermore, specific thermal conductivities of bio-based and bio-sourced materials: bagasse (0.046-0.055 W m\({}^{-1}\) K\({}^{-1}\)), kenaf (0.034-0.043 W m\({}^{-1}\) K\({}^{-1}\)), and pineapple-leaf fibers (0.035-0.042 W m\({}^{-1}\) K\({}^{-1}\)) are not far from those of conventional man-made materials like mineral wool (0.033-0.040 W m\({}^{-1}\) K\({}^{-1}\)) and expanded polystyrene (0.031-0.038 W m\({}^{-1}\) K\({}^{-1}\)) [7]. Thermal conductivities demonstrated by some of the unconventional materials were lower than 0.1 W m\({}^{-1}\) K\({}^{-1}\); in case banana and polypropylene (PP) commingled yarn, the highest thermal conductivity results (0.157-0.182 W m\({}^{-1}\) K\({}^{-1}\)) were reported. Due to anatomical structure of the hollow plant fibers, their thermal conductivities and heat capacities are significantly influenced by the sample's exposure towards heat flow from the source [18].