## 1 Introduction  
Low-birth-weight and preterm neonates are particularly at risk of body cooling. Hypothermia can lead to hypoglycemia, respiratory distress, hypoxia, and metabolic acidosis and is associated with greater morbidity and mortality rates [1,2]. Thermal regulation is less effective than in adults due to the immaturity of the neonate's organs and greater body heat losses to the environment [3]. During cold exposure, the energy used to maintain homeothermy depletes that available for vital functions. These factors are especially important for premature and low-birth-weight neonates. To prevent neonatal hypothermia immediately after delivery, skin-to-skin care (SSC) is recommended by the World Health Organization (WHO) [4]. In 2017, the WHO recommended that in the absence of medical contraindications, a newborn should be dried, placed naked in the prone position on the mother's chest, covered with a clean, warm cloth and a cap, and left in contact for an hour [5]. The WHO has further stated that SSC is an effective method for preventing body heat losses in term or premature neonates [6]. Several studies of term neonates have shown that SSC is enough to warm the neonate after delivery and avoids the need for other warming methods (e.g., radiant warmers and incubators). [PERSON] [7] showed that early skin-to-skin contact under a warm blanket (preceded by drying of the skin) enabled neonates to maintain their internal body temperature. [PERSON] et al. (2018) showed that axillary and skin temperatures were higher in infants placed in contact with their mothers for 90 min immediately after birth. In [PERSON] et al. 's infrared thermography study [PERSON] et al. (2018), skin surfaces in contact with the mother were warmer than those not in contact. [PERSON] et al. (2018) claimed that SSC was equivalent to placing the neonate in a closed incubator. In a study in India, [PERSON] et al. (2018) showed that SSC stabilized the neonate's thermal status and increased the breastfeeding rate and the sucking reflex. [PERSON] et al. (2018) showed that in premature neonates, cold stress decreased when the delivery room air temperature (T\({}_{\text{a}}\)) was maintained at 25 \({}^{\circ}\)C (i.e., the value recommended by the WHO). In a study in Croatia, [PERSON] et al. (2018) demonstrated that when T\({}_{\text{a}}\) was 21.7 \({}^{\circ}\)C, SSC was effective for maintaining homethermy in neonates born after 38 weeks of amenorrhoea but not in those born more prematurely. These research findings demonstrated the importance of the T\({}_{\text{a}}\) and the neonate's maturity in the management of the thermal environment at birth. The effectiveness of SSC also depends on (i) the thermal insulation provided by the cloth, sheet, or clothing covering the mother and the neonate and (ii) the neonate's metabolism--the main source of heat production in response to cold stress. The degree of thermal insulation that must be provided by the cloth placed on the neonate during SSC has not been defined, even though this is a particularly important factor in reducing body heat losses. With the exception of [PERSON] (2018), researchers in this field have not reported the degree of thermal insulation provided by the cloth or sheet used in SSC; they simply recommend adapting this variable to the ambient temperature. There are no guidelines on the optimal thermal properties of coverings or clothing for premature newborns during SSC. To address this problem, we used a physical model (a thermal mannequin, as recommended in the ISO 9920 standard for assessing the impact of the thermal isolation of a set of clothes on body heat exchanges) ([PERSON] et al., 2018). As reported by many researchers, metabolic heat production varies greatly from one individual to another. [PERSON] et al. (2018) measured oxygen consumption in 75 premature infants (gestational age: between 26 and 28 weeks) during the first week of life: the individual values ranged from 1.11 W/kg to 2.70 W/kg (mean: 1.59 W/kg).