## 1 Introduction  
The materials used for insulation and thermoregulation are typically made of multi-layer materials consisting of two outer layers and an inner padding traditionally made from goose or duck feathers [1]. These are light and compressible products in which thermal insulation is obtained by exploiting the feather's ability to trap the air, which is widely known as one of the best thermal insulators [2]. Unfortunately, in the presence of moisture, the thermal insulation for such products is drastically reduced--if the padding is exposed to water and the surface fabric is not properly isolated, the thermal insulation drops to zero [3]. Moreover, multilayer materials filled with feathers are expensive and, often, the origin of natural material often involves the presence of impurities or substances dangerous to health. The scientific and technological attention of the Textile sector has therefore shifted towards multi-layer products filled with synthetic materials (i.e., thermal padding). In particular, a sufficient mix of textile fibers and air is achieved to guarantee the desired thermal insulation by using a series of superimposed layers of soft, very low-density carded fibers [4]. This technology makes it possible to produce products such as, for instance, down jackets that are generally less expensive than the ones made of goose plumes--at the same time, multi-layered products padded with fibers may be rendered hypoallergenic, washable, and water-resistant. However, the injected materials are subject to poor stability even after a short time of use or after a few washesbecause they tend to form lumps, \"voids\", or leakage of the fibers from the layers of support with a significant reduction in the thermal characteristics of the finished product [5]. Furthermore, for these products there subsists a linear correlation between the thickness of the insulating layer and the thermal insulation characteristics of the finished product, which results in high thicknesses. The thickness reduction of padded fabrics (preserving their thermal insulation capacity) is still a subject of study both in scientific literature [6; 7; 8; 9] and in the market, as also demonstrated by a large and growing number of brands and products for padding obtained by appropriately mixing synthetic fibers. Not by chance, considerable progress was made in recent years in several commercial products on the structure of the internal padding. PrimaLoft(r), designed for the US Army, was the first product in which microfibers were used to optimize the ratio between heat and weight of the insulation material. From this foreruner, there are now numerous products in which the thermal wadding is obtained with synthetic materials optimized in terms of weight and size by testing numerous combinations of fibers: Polarguard(r), Heatseeker(tm), Thinsulate(r), Lite Loft(tm), Thermolite(r), Thermoloft(r), Corelof(tm), ThermaTek(tm), and Thermogen(r)[10]. To date, the best commercial product able to guarantee thermoregulation using thermal wadding is Thermore(r) for which a particular production process has been developed, called SR, which allows reducing the thickness of the padding without significantly altering the thermal performance since the process reduces the thickness but not the amount of air trapped in the structure. However, all state of the art products encompass a three-layer structure comprising two outer fabrics (with variable characteristics such as impermeability/permeability, resistance to friction, etc.) and a padding/system used for insulation (see Figure 1). A possible alternative to the traditional three-layer product, which could also partially fulfill the function of thermoregulation, is the non-woven fabric; although its water-repellent properties and, if made at low density, its thermal insulation characteristics, this type of fabric has never been used for designing fashion fabrics, mainly due to its unsophisticated appearance [11].