The prevalence of hypothermia across low-resource settings is high, especially in countries with high neonatal mortality rates. If left untreated, hypothermia can additionally result in a significant comorbidity, and has been linked to a reduction in the effectiveness of treatment for other newborn conditions. Effective thermal care for hypothermic newborns is not widely available in low-resource settings due to cost of consumables and spare parts. In this study, the research team wish to evaluate the efficacy of a novel neonatal warming mattress in treating hypothermic newborns. Warming mattress, 'Celsi Warmer', has been developed by Rice 360 Institute for Global Health Technologies, in conjunction with African clinicians, to be a robust, low-cost, and easy-to-use warming mattress which can address the challenges of hypothermia. This is a single-arm, non-randomized, prospective intervention study. Up to 90 eligible infants at the neonatal wards of the Lagos University Teaching Hospital will be recruited to evaluate the efficacy of Celsi Warmer in rewarming hypothermic newborns. Infants temperature will be monitored during thermal intervention and the performance of the device will be evaluated. The temperatures of each infant will be compared before, during, and after the intervention.

Inclusion Criteria:

Any neonate who:

1. Is currently being treated at study location,
2. Is an inborn admission to the neonatal ward,
3. Whose parents or guardians provided informed consent,
4. Whose parents or guardians providing informed consent are 18 years old or older,
5. Has a current weight of greater than or equal to 1.0 kg and less than or equal to 4.0 kg,
6. Has been identified as in need of thermal care defined as having a moderate to severe hypothermic temperature (32.0-36.0 °C) as the last temperature recorded in hospital chart, or during recruitment procedures; and
7. is unable to be enrolled in Kangaroo Mother Care (KMC) for reasons including, but not limited to: a. Mother/guardian unable or unavailable to provide KMC b. Under observation in the Neonatal Intensive Care Unit (NICU) before transfer to KMC c. No space in KMC d. Clinician's discretion;
8. May be receiving other medical treatments, including but not limited to, Continuous Positive Airway Pressure (CPAP), oxygen therapy, intravenous (IV) fluids, management and monitoring of common newborn conditions such as hypoglycemia, and/or hyperbilirubinemia.

Exclusion Criteria:

1. Requires mechanical ventilation;
2. Is deemed in need of intensive care by the hospital staff who is providing care, including but not limited to: a. neonates with severe anemia and/or any suspected hematological disorders, and/or b. Neonates with obvious congenital anomalies, and/or c. neonates suspected with hypo/hyperthyroidism or any hormonal disorders;
3. has been diagnosed with birth asphyxia;
4. Presents a condition that precludes the use of the temperature sensor and/or abdominal belt including but not limited to, known umbilical cord infection, known skin infection;
5. Whose clinician presents concerns about their participation;
6. Is receiving treatment that participation in the study would interfere with (e.g. transferring to KMC).