A radiant warmer is an open-bed heating device that uses infrared energy to keep a newborn’s body temperature stable during the critical first minutes and hours after birth. In hospitals around the world, it is one of the most common pieces of equipment in delivery rooms and neonatal intensive care units. The device offers a significant practical advantage: because it is open from above, doctors and nurses can immediately access the baby for resuscitation, procedures, or monitoring without interrupting the heat supply. That openness, though, comes with trade-offs, particularly around fluid loss, that shape how clinicians manage care around it.
Why Newborns Need External Heat
Babies lose heat fast. A newborn’s surface area relative to body weight is much larger than an adult’s, and their skin, especially a premature baby’s skin, offers less insulation. Within minutes of leaving the warm, wet environment of the womb, a baby can lose heat through evaporation of amniotic fluid, radiation to cooler room surfaces, convection from air currents, and direct contact with cold surfaces. Hypothermia in newborns is not just uncomfortable; it increases oxygen demand, burns through glucose stores, and in preterm or sick infants can contribute to serious complications. Maintaining a stable core temperature, typically between about 36.5°C and 37.5°C, is one of the first priorities in newborn care.
How a Radiant Warmer Works
The device looks like a bassinet or flat bed positioned beneath an overhead heating element. That element emits infrared radiation, the same type of invisible heat you feel from a fireplace or a warm stone wall. The infrared energy passes through the air without warming it much and is absorbed directly by the baby’s skin and clothing, warming the infant from the outside in. A skin temperature sensor, usually taped to the baby’s abdomen, feeds real-time data back to the machine. In servo-control mode, the warmer continuously adjusts its heat output to keep the baby’s skin at a set target temperature. In manual mode, the clinician selects a fixed power output and monitors the baby’s temperature separately.
The servo-control approach matters because radiant warmers from different manufacturers can produce meaningfully different exposure temperatures even at the same power setting. Research comparing commercially available devices found that the temperature a baby actually experiences under a radiant warmer varies significantly from one brand to another, which means a baby could be at risk of either getting too cold or overheating if staff rely on a fixed manual setting without close monitoring.1PubMed. Effective temperature under radiant infant warmer: does the device make a difference? Servo-control eliminates much of that variability by responding to the baby’s actual temperature rather than relying on a preset output level.
The Delivery Room Advantage
The radiant warmer’s defining feature is that it is open. In the delivery room, this is a major benefit. When a baby is born needing help, whether it is gentle stimulation, suctioning, or full resuscitation with positive-pressure ventilation, the care team needs immediate, unobstructed access. An enclosed incubator would require opening porthole doors or lifting a canopy, which costs precious seconds and can disrupt the thermal environment. A radiant warmer lets multiple clinicians work around the baby simultaneously while heat continues to pour down from above.2PubMed Central. Neonatal warming devices: What can be recommended for low-resource settings when skin-to-skin care is not feasible?
For this reason, nearly every delivery room in a well-equipped hospital has a radiant warmer pre-heated and ready. Even healthy term babies are often briefly placed under one for initial assessment, drying, and the first few minutes of life before transitioning to skin-to-skin contact with a parent. For babies who need more extensive stabilization, the warmer serves as the resuscitation workstation for as long as needed.
The Fluid Loss Problem
The radiant warmer’s open design, which is so useful for access, creates its most well-known drawback. Because there is no enclosure trapping humidity around the baby, water evaporates from the infant’s skin more readily. This is called insensible water loss, the water your body loses through the skin and lungs that you do not notice as sweat. Under a radiant warmer, that loss increases substantially.
One of the earliest studies on this, published in what is now JAMA Pediatrics, measured insensible water loss in newborns under radiant warmers versus standard convection-heated incubators. Babies under the radiant warmer lost water at roughly twice the rate: about 1.08 grams per kilogram per hour, compared to 0.53 grams per kilogram per hour in incubators.3JAMA Pediatrics. Effects of Radiant Warmer on Insensible Water Loss in Newborn Infants A Cochrane systematic review confirmed the finding, reporting a statistically significant increase in insensible water loss with radiant warmers compared to incubators, and noted that this needs to be factored into daily fluid calculations.4Cochrane Database of Systematic Reviews. Radiant warmers versus incubators for regulating body temperature in newborn infants
For a healthy full-term baby who spends only a short time under the warmer, the extra fluid loss is clinically trivial. The concern becomes real for very low birth weight and extremely premature infants, whose skin is thinner and more permeable, and who may spend days or even weeks under open radiant heat. In those babies, the increased evaporative loss can disrupt fluid and electrolyte balance, requiring careful monitoring and adjustments to intravenous fluid intake.5PubMed. Radiant energy and insensible water loss in the premature newborn infant nursed under a radiant warmer
Reducing Evaporative Loss with Plastic Wraps and Other Strategies
Clinicians have developed several practical workarounds to curb the fluid loss problem while still using radiant warmers. The simplest and most widely studied is wrapping the baby in a thin plastic film, similar to household cling wrap, without first drying off the amniotic fluid. The plastic creates a barrier that traps moisture close to the skin and dramatically reduces evaporation.
A randomized controlled trial in very low birth weight babies found that those nursed under a radiant warmer with cling wrap had significantly better temperature stability: none of the wrapped babies developed hypothermia during the first seven days, compared to 36% of the unwrapped group. Babies who arrived already hypothermic also rewarmed faster when wrapped. Weight loss in the first 48 hours, a rough proxy for fluid loss, trended lower in the wrapped group as well.6PubMed. Cling wrap, an innovative intervention for temperature maintenance and reduction of insensible water loss in very low-birthweight babies nursed under radiant warmers: a randomized, controlled trial
Modern neonatal practice often bundles several interventions together: keeping the delivery room temperature between about 23°C and 25°C, applying a plastic wrap immediately, placing a knitted cap on the baby’s head, using a chemical warming mattress underneath, and positioning the baby under the radiant warmer. When all of these are combined, studies show good temperature stability without a notable increase in overheating.7NeoReviews. Thermoregulation: Advances in Preterm Infants The wrap-plus-warmer approach has become standard in many NICUs, especially for infants born before 32 weeks.
Radiant Warmer Versus Incubator for Longer-Term Care
Once the initial stabilization period is over, the question arises: should a preterm baby stay under the radiant warmer or move into a closed incubator? Incubators hold humidity better, which addresses the fluid loss issue, and they shield the baby from drafts and ambient noise to some degree. On the other hand, they make it harder for staff to reach the baby quickly and can feel more isolating for parents.
A clinical trial comparing radiant warmer care with incubator care for preterm infants from birth until they reached 1,800 grams found no significant difference in daily weight gain (about 17 grams per kilogram per day in both groups), time to regain birth weight, or length of hospital stay.8PubMed. A clinical comparison of radiant warmer and incubator care for preterm infants from birth to 1800 grams That finding surprised some clinicians who expected the higher insensible water loss under warmers to translate into slower growth. In practice, the extra fluid given to warmer-group infants to compensate for evaporative losses appears to have balanced things out.
The Cochrane review on this comparison, while confirming the increased insensible water loss with radiant warmers, found that the number of participants across existing studies was too small to draw firm conclusions about whether the fluid loss difference actually worsens outcomes like oxygen consumption, morbidity, or mortality.9PubMed Central. Neonatal warming devices: What can be recommended for low-resource settings when skin-to-skin care is not feasible? In other words, the physiological difference is real and measurable, but whether it ultimately matters for the baby’s health depends heavily on how well the clinical team adjusts fluid management.
Most NICUs use a hybrid approach. A baby might spend the first hours under a radiant warmer for stabilization and procedures, then transition to an incubator once the need for frequent hands-on access decreases. The warmer comes back out whenever the baby needs a procedure, line placement, or other intervention that requires open access.
Skin-to-Skin Contact as an Alternative
Kangaroo mother care, or skin-to-skin contact, is the oldest warming method in the world and remains remarkably effective. The parent’s chest acts as a responsive heat source, naturally adjusting to the baby’s needs in ways no machine can replicate. Beyond temperature regulation, skin-to-skin contact promotes breastfeeding, stabilizes heart rate and breathing, and supports behavioral organization in the newborn. Research comparing the two approaches shortly after birth suggests that kangaroo care influences the baby’s state regulation and physiological stability in ways a warmer does not match.10Journal of South Asian Federation of Obstetrics and Gynaecology. Comparison of Radiant Warmer Care and Kangaroo Mother Care Shortly after Birth on the Neurobehavioral Responses of the Newborn
That said, skin-to-skin care is not always feasible. If the baby needs resuscitation, intravenous access, respiratory support, or close monitoring, a radiant warmer is the practical choice. And for moderate to late preterm infants, a randomized trial found that while immediate skin-to-skin contact produced similar clinical stability scores at 60 minutes compared to radiant warmer care, body temperature was slightly but significantly lower in the skin-to-skin group (about 36.4°C versus 36.6°C).11PubMed. Immediate skin-to-skin contact versus care under radiant warmer at birth in moderate to late preterm neonates – A randomized controlled trial The difference is small and stayed within normal range, but it underscores why some units prefer to start borderline preterm infants under a warmer first, especially in cooler delivery rooms, and transition to skin-to-skin once the baby’s temperature is confirmed stable.
The two approaches are not in competition. In practice, the radiant warmer handles the minutes when medical access is the priority, and skin-to-skin takes over when the baby is stable and the parent is ready. Many hospitals now encourage skin-to-skin as early as possible, even in the NICU, using the warmer only when procedures or instability demand it.
What Parents See and What It Means
If your baby ends up under a radiant warmer after birth, it can look alarming. The infant is lying on a flat, open platform, often naked or wearing just a diaper, with a sensor taped to the belly and the overhead heater glowing. It looks clinical and exposed compared to a swaddled baby in a bassinet. But the openness is the point. It means the care team can see, touch, and assess the baby instantly, and the baby is being kept warm the entire time.
The temperature probe on the baby’s abdomen is what the machine uses to make its heating decisions in servo mode. If that probe comes loose or gets sandwiched between the baby and the mattress, the warmer can misread the temperature and either overheat or underheat the infant. Nurses watch for this carefully, but if you notice the probe seems displaced while visiting your baby, it is worth mentioning.
You may also see a plastic wrap or bag covering your baby’s body under the warmer, especially if the baby was born prematurely. This is not packaging. It is an evidence-based intervention to prevent heat and fluid loss while the warmer does its job. The wrap stays on until the baby’s temperature has stabilized and the transition to an incubator or skin-to-skin is ready.
The Noise and Sensory Environment
One concern that occasionally comes up is whether a baby under a radiant warmer is exposed to more noise than one inside a closed incubator. The incubator’s walls might seem like they would muffle sound. Research measuring actual sound pressure levels found that the noise from monitor alarms and crying inside an incubator was not significantly different from levels measured under a radiant warmer.12PubMed. Noise levels in neonatal intensive care unit and use of sound absorbing panel in the isolette In other words, the incubator walls do not provide the acoustic shielding parents might assume. The NICU is a noisy environment regardless of which warming device is in use, and reducing harmful noise exposure requires broader unit-level changes like quieter alarm settings and staff awareness rather than a choice between warmer and incubator.
Low-Resource Settings and Global Access
Radiant warmers require a reliable electricity supply, periodic maintenance, and trained operators. In many low-resource settings, these requirements pose real barriers. Power outages can leave a baby suddenly without heat, and devices that malfunction without access to biomedical engineering support become expensive furniture. This is one reason global health organizations have invested so heavily in promoting kangaroo mother care: it works, it costs nothing, and it requires no electricity.
When skin-to-skin care is not possible, however, and resources for closed incubators are limited, radiant warmers still offer a practical warming solution for delivery rooms where a baby needs stabilization. The short-term use case in the delivery room, where the warmer keeps the baby warm during the minutes of initial assessment and resuscitation, is where the device arguably provides the most benefit relative to its cost and complexity.13PubMed Central. Neonatal warming devices: What can be recommended for low-resource settings when skin-to-skin care is not feasible? The challenge comes with prolonged use in settings where fluid monitoring and intravenous access are not reliably available, since the increased insensible water loss cannot be easily compensated.
When Overheating Becomes the Risk
Most of the conversation around radiant warmers focuses on preventing hypothermia, but overheating is a real and underappreciated danger. When the servo-control probe falls off the skin or is poorly positioned, the warmer may read a falsely low temperature and crank up the heat output. A baby under full radiant power with a malfunctioning sensor can develop hyperthermia quickly. Even when equipment is functioning normally, placing additional blankets or thick clothing on a baby under a radiant warmer can trap heat and push the temperature too high.
The variation in heat output among commercially available devices adds another layer of risk. Without servo control, selecting a manual power level based on experience with one brand of warmer could produce dangerously different results on another.14PubMed. Effective temperature under radiant infant warmer: does the device make a difference? This is why current best practice emphasizes servo-controlled modes with properly placed skin sensors for anything beyond very brief periods of manual warming during initial resuscitation.
The combined bundled approach described earlier, using plastic wraps, caps, and warming mattresses together under the radiant warmer, was specifically studied with an eye toward whether it pushed babies into hyperthermia. The evidence shows that it does not, as long as the interventions are used according to protocol and temperature monitoring is continuous.15NeoReviews. Thermoregulation: Advances in Preterm Infants Still, nursing vigilance remains the real safety net. No machine replaces an attentive clinician watching the numbers.
How Fluid Management Adjusts Around the Warmer
For babies spending extended time under a radiant warmer, clinical teams typically increase daily fluid intake to offset the higher insensible water loss. The exact adjustment depends on the baby’s gestational age, birth weight, skin maturity, and whether barriers like plastic wraps are being used. A 26-week preterm infant with paper-thin skin will lose far more fluid than a 35-week infant with more developed skin layers, so the fluid prescription is individualized.
Clinicians track urine output, body weight changes, serum sodium levels, and overall hydration status to fine-tune the fluid plan. If sodium starts creeping up, it often signals that the baby is losing more water than anticipated, prompting an increase in fluids. This is a routine part of neonatal intensive care, and the radiant warmer simply shifts the baseline fluid calculations upward compared to what would be needed in an incubator.16PubMed. Radiant energy and insensible water loss in the premature newborn infant nursed under a radiant warmer
For parents, this may look like the baby receiving more IV fluids than expected, or the care team being particularly attentive to weighing diapers and tracking every milliliter going in and out. It can feel excessive, but it reflects the known physiology of open radiant heat and the team’s effort to stay ahead of a predictable problem.