Quick Answer: PCM (phase change material) absorbs heat by transitioning between solid and liquid states. Graphite-infused foam conducts heat laterally away from your body. PCM moderates initial heat spikes; graphite provides consistent passive cooling. Neither performs well if the underlying mattress traps heat. Pocket coil construction underneath makes a bigger difference than either material alone.
In This Guide
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How Phase Change Material Works
Phase change materials exploit a physical property that most people last encountered in high school chemistry: when a substance transitions between solid and liquid states, it absorbs or releases a significant amount of heat without changing temperature. Ice melting is the everyday version. You can add heat energy to a glass of ice water and the temperature stays at zero degrees Celsius until all the ice is gone, because the energy goes into breaking the ice's crystal structure rather than raising the temperature.
PCM used in mattresses works on the same principle, but with substances that have phase change points near skin temperature, roughly 28 to 32 degrees Celsius. When your body heats the PCM above its transition temperature, it absorbs that heat and liquefies. The material next to your skin does not feel warmer because the heat is being stored in the phase transition rather than raising the material's temperature. When you shift position or the room cools, the PCM re-solidifies and releases that stored heat.
In practice, PCM is either encapsulated into tiny beads and suspended in foam, or coated onto the surface fibres of a mattress cover. The encapsulated version is generally more durable because the phase change happens inside the protective shell, preventing leakage as the material cycles. Cover-coated PCM is common in budget versions and may diminish in effectiveness after repeated washing.
Why Body Temperature Matters for Sleep Quality
The relationship between body temperature and sleep onset is well established. Kräuchi (2007), reviewing circadian temperature regulation in Sleep Medicine Reviews, notes that the process of falling asleep is directly associated with peripheral vasodilation and heat loss from the skin. Body core temperature drops naturally in the hour before sleep, and any material that impedes that heat dissipation delays sleep onset and increases arousal events. Okamoto-Mizuno and Mizuno (2012) confirmed in Journal of Physiological Anthropology that both elevated and lowered thermal environments reduce sleep quality and increase body movement during the night. A mattress cover or comfort layer that prevents normal heat dissipation creates exactly the conditions associated with poor sleep quality in both studies.
How Graphite-Infused Foam Works
Graphite has among the highest thermal conductivity of any non-metallic material. When graphite particles are distributed through a foam matrix, they create heat pathways that move thermal energy laterally and downward through the foam rather than allowing it to pool at the body-foam interface. This is passive heat transfer: no phase change, no absorption into a material state transition. The graphite simply conducts heat away from the contact zone continuously.
The practical implication is that graphite foam has no "saturation" point. It cannot absorb heat until it is full and then stop working. As long as there is a temperature gradient (your body warmer than the mattress beneath), heat continues to move away from you through the graphite pathways. The rate of transfer depends on how much temperature differential exists and how well the heat can escape from the underside of the foam into the coil system or base below.
This is why graphite foam performs significantly better over a pocket coil core than over a dense all-foam base. The coil system allows air movement, providing a heat sink for the graphite to conduct toward. Put graphite foam on top of dense memory foam with no air movement, and the graphite's efficiency drops because there is nowhere for the heat to go once it reaches the bottom of the graphite layer.
The Honest Comparison: Strengths and Limits
PCM vs Graphite: What Each Does Well
- PCM - Strength: Buffers rapid heat spikes. If you get into bed at a warm body temperature, PCM absorbs that initial heat load quickly and creates a noticeably cool surface sensation. Good for people who run very hot for the first 60 to 90 minutes of sleep.
- PCM - Limit: Once saturated, it needs to re-solidify before absorbing more heat. If your bedroom is warm and you stay hot all night, the PCM may stay in liquid state and provide no further benefit after the initial absorption. Cover-coated PCM in cheap mattress covers degrades over time and washing cycles.
- Graphite - Strength: Continuous, consistent conduction. No saturation. Performs steadily through the night rather than offering bursts of cooling followed by diminished effect. Also helps distribute heat more evenly across the sleeping surface, reducing hot spots.
- Graphite - Limit: The cooling effect depends on having somewhere for the heat to go. Over a solid foam base, effectiveness is greatly reduced. Does not provide the initial "cold touch" sensation that PCM cover treatments do. Less effective for that first few minutes of contact.
- Both technologies: Perform better in a cool bedroom. A room at 22 degrees Celsius will allow more heat dissipation than a room at 28 degrees regardless of what the mattress surface does. Room temperature management matters more than mattress cooling technology for severe hot sleepers.
Brad tends to be direct with customers about this comparison. "Both technologies help," he says, "but neither one is a substitute for a breathable mattress construction underneath them. We've seen people spend extra money on a PCM cover on an all-foam bed and then wonder why they're still hot. The foam block underneath was trapping everything."
Canadian Climate Considerations
Canadian summers, particularly in the Southern Ontario corridor where Brantford sits, can push bedroom temperatures into the mid-to-upper 20s Celsius for several months. During those months, cooling mattress technologies provide genuine benefit for hot sleepers.
But Canada also has long, cold winters. PCM has a useful property in cold conditions that graphite does not: when you first get into a cold bed, the PCM (which re-solidified during the day as the room cooled) will release some of its stored heat as it returns to room temperature, gently warming the sleeping surface. This is not dramatic, but some sleepers notice it as a slight warmth when they first lie down in a cold room in January. Graphite, being passive, simply conducts whatever temperature differential exists at that moment, which in a cold room may mean conducting cold upward initially.
For year-round temperature management in Canada, PCM in the cover or top comfort layer combined with graphite in the deeper comfort layer is a reasonable combination: the PCM handles the initial thermal exchange at skin contact, and the graphite moves heat through the layer stack toward the coil core. Our Restonic Luxury Silk and Wool Queen at $1,395 takes a different but complementary approach, using natural wool's moisture-wicking and temperature-regulating properties instead of synthetic PCM or graphite, which is worth considering for those who prefer natural material solutions.
What Actually Matters More Than Either
The Construction Underneath Changes Everything
In our experience testing mattresses in Brantford over many years, the single biggest determinant of whether a mattress sleeps cool is the support core construction, not the cooling material in the comfort layer. A pocket coil system with 1,200+ individually wrapped springs allows air to circulate through the core. Heat that moves down from your body through the comfort layer has somewhere to go. An all-foam mattress with a PCM cover can feel cool on contact but then still trap heat within its dense foam structure. If you are a genuine hot sleeper, the conversation should start with the core construction before we even get to PCM versus graphite. The cooling materials are the finishing touch on a breathable system, not the solution to a heat-trapping one.
Cooling Mattresses in Brantford Summers
Brantford's proximity to the Grand River and its basin means summer humidity can run higher than people expect, which amplifies the effects of heat-trapping mattresses significantly. High humidity at the skin-mattress interface makes any lack of moisture wicking feel worse and raises perceived temperature. The combination of a breathable pocket coil core and a natural moisture-wicking comfort layer (wool, cotton, or Talalay latex) handles both heat and humidity better than synthetic cooling technologies alone. If you have been sleeping hot in Brantford summers and have tried gel and PCM covers without relief, come talk to us about the construction underneath. That conversation changes the outcome much more reliably than switching between cooling layer technologies.
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Cooling picks we carry at Mattress Miracle:
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Find Your Perfect Mattress at Mattress Miracle
We are a family-owned mattress store in Brantford, helping our community sleep better since 1987. Come try mattresses in person and get honest, no-pressure advice.
441 1/2 West Street, Brantford, Ontario
Call 519-770-0001Frequently Asked Questions
Does PCM in a mattress cover wash out over time?
It depends on how the PCM is applied. Encapsulated PCM embedded in foam is protected inside a polymer shell and is not affected by washing. PCM coated onto the surface fibres of a mattress cover will degrade with repeated washing. Most mattress covers with PCM should not be machine washed frequently. Check the manufacturer's instructions. If your mattress has a removable, washable cover with PCM coating, expect the cooling effect to diminish over two to three years of regular washing.
Is graphite foam toxic or safe to sleep on?
Graphite-infused foam used in certified mattresses is safe. The graphite particles are suspended within the foam matrix and are not in contact with the sleeper's skin. Look for CertiPUR-US certification on the foam, which tests for harmful chemicals including VOCs, heavy metals, and off-gassing. Graphite itself is non-toxic. The concern with foam mattresses is other chemicals, not the graphite additive.
Which cooling technology is better for menopause night sweats?
Neither alone is sufficient for severe night sweats. Night sweats from menopause are a hormonal event that produces significant moisture and heat output, more than passive mattress cooling can fully absorb. A combination approach works best: a breathable pocket coil core for air circulation, natural moisture-wicking fibres (wool or cotton) in the comfort layer, and a washable mattress protector that can be changed if needed. PCM may help buffer the initial heat spike, but a mattress cover that wicks moisture is at least as important for night sweat comfort.
Can I add graphite foam or PCM to my existing mattress?
You can add a mattress topper with graphite or PCM materials to an existing mattress. The limitation is the same: if the mattress underneath is a dense foam construction that traps heat, the topper will be fighting the heat from below. A graphite or PCM topper on a breathable mattress will be noticeably more effective than the same topper on a hot-sleeping all-foam bed. Our showroom has toppers you can test and compare.
Does Mattress Miracle in Brantford carry mattresses with PCM or graphite cooling?
Yes. Several models in our Restonic lines include graphite-infused foam comfort layers and breathable cover treatments. Come into our showroom at 441 1/2 West Street in Brantford and Dorothy can walk you through the construction of each cooling model. We are honest about what the technology actually does and will not oversell it if a simpler breathable construction will serve your needs better. Call us at (519) 770-0001 to discuss before your visit.
Sources
- Kräuchi, K. (2007). The thermophysiological cascade leading to sleep initiation in relation to phase of entrainment. Sleep Medicine Reviews, 11(6), 439-451. doi.org/10.1016/j.smrv.2007.07.009
- Okamoto-Mizuno, K., & Mizuno, K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 31(1), 14. doi.org/10.1186/1880-6805-31-14
- Jacobson, B.H., Boolani, A., & Smith, D.B. (2008). Changes in back pain, sleep quality, and perceived stress after introduction of new bedding systems. Journal of Chiropractic Medicine, 8(1), 1-8. doi.org/10.1016/j.jcme.2008.09.002
- Zhang, N., Yuan, Y., Cao, X., et al. (2017). Latent heat thermal energy storage system with constant temperature output: A review. Applied Thermal Engineering, 123, 1345-1363. doi.org/10.1016/j.applthermaleng.2017.05.205
- Shin, M., Halaki, M., Swan, P., et al. (2016). The effects of fabric for sleepwear and bedding on sleep at ambient temperatures of 17°C and 22°C. Nature and Science of Sleep, 8, 121-131. doi.org/10.2147/NSS.S100271
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Mattress Miracle , 441½ West Street, Brantford, ON · (519) 770-0001
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