Quick Answer: Support factor (SAC) measures how well foam resists compression under load. Poly-foam typically has a support factor of 1.8 to 2.8, while memory foam ranges from 2.0 to 3.5. Higher support factor means better long-term durability and less bottoming out. Visit Mattress Miracle in Brantford to feel the difference in person.
In This Guide
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What Is Support Factor (SAC)?
Support factor, sometimes called Support Area Compliance or SAC rating, is a measurement that describes how foam behaves under increasing pressure. It is the ratio of the force needed to compress foam to 65% of its original height divided by the force needed to compress it to 25%.
In simpler terms, it tells you how quickly the foam firms up as you press deeper into it. A foam with a high support factor feels soft on the surface but gets progressively firmer the deeper you sink. A foam with a low support factor feels more uniform throughout, meaning it does not resist much more at the bottom than at the top.
Why does this matter? Because when you lie on a mattress, your body's heaviest points (hips, shoulders) press deeper into the foam than lighter areas. A foam with good support factor cradles those pressure points on the surface while providing increasing resistance underneath. This prevents the "hammock effect" where you sink too deep and wake up with back pain.
The Physics of Foam Compression
Support factor is derived from IFD (Indentation Force Deflection) testing. IFD measures the force in pounds required to compress a foam sample by a specific percentage. IFD at 25% is the "surface feel" rating, while IFD at 65% represents deep compression support. The ratio between these two numbers is the support factor. For mattress comfort layers, a support factor of 2.0 or higher is generally considered good quality.
Poly-Foam Explained
Polyurethane foam, commonly called poly-foam, is the most widely used foam in mattress construction. It appears in everything from budget mattresses to luxury models, though in different densities and formulations.
Types of Poly-Foam
Conventional poly-foam (density below 1.5 lb/ft3) is the basic cushioning material. It is affordable and provides initial comfort, but tends to break down faster. You will find it in budget mattress comfort layers and as padding under quilted covers.
High-density poly-foam (density 1.8 to 2.5 lb/ft3) is more durable and offers better support. It is commonly used as a transition layer between the comfort layer and the coil system. At Mattress Miracle, the mattresses we carry use higher-density foams because they hold up much better over time.
High-resilience (HR) poly-foam (density 2.5+ lb/ft3) is the premium tier. It has excellent support factor ratings, typically 2.4 to 2.8, and bounces back quickly when pressure is removed. HR foam feels responsive rather than sinking.
Poly-Foam Support Factor Range
Most conventional poly-foam has a support factor between 1.8 and 2.4. High-resilience poly-foam reaches 2.4 to 2.8. The higher numbers indicate foam that will maintain its comfort and support characteristics longer.
Memory Foam Explained
Memory foam (viscoelastic polyurethane foam) was originally developed by NASA for seat cushioning. It responds to body heat and pressure, conforming closely to your shape and distributing weight evenly across the sleep surface.
How Memory Foam Differs
The key difference between memory foam and poly-foam is the response time. When you press into memory foam, it slowly conforms to your shape and holds that impression. When you release, it gradually returns to its original form. Poly-foam responds and recovers almost immediately.
This slow response is what gives memory foam its pressure-relieving properties. It cradles the body's contours rather than pushing back against them. For people with joint pain, pressure sores, or spinal alignment issues, this conforming quality can make a noticeable difference.
Memory Foam Support Factor Range
Quality memory foam typically has a support factor between 2.0 and 3.5. The higher support factor in memory foam comes from its viscoelastic properties. It is soft and conforming at the surface but progressively firmer deeper in the material. This makes it particularly good at preventing bottoming out for heavier sleepers.
"A lot of customers come in thinking all memory foam is the same," Brad notes. "But the difference between a 3-pound density memory foam and a 5-pound density memory foam is dramatic. The higher density foam has better support factor and lasts years longer."
Side-by-Side Comparison
Poly-Foam vs Memory Foam at a Glance
- Support Factor Range: Poly-foam 1.8-2.8, Memory foam 2.0-3.5
- Response Time: Poly-foam is immediate, memory foam is slow (3-10 seconds)
- Pressure Relief: Memory foam excels, poly-foam is good but less conforming
- Heat Retention: Memory foam retains more heat, poly-foam breathes better
- Durability: Both depend on density, higher density lasts longer in either type
- Motion Isolation: Memory foam is superior, poly-foam transfers more motion
- Price: Poly-foam is generally less expensive, quality memory foam costs more
- Bounce: Poly-foam bounces back quickly, memory foam has minimal bounce
Which Has Better Support Factor?
On average, memory foam edges out poly-foam in support factor ratings. But there is significant overlap. A high-resilience poly-foam at 2.6 support factor outperforms a basic memory foam at 2.0. The foam type matters less than the specific formulation and density.
The Role of Density
Density is the single best predictor of both support factor and durability. For poly-foam, look for at least 1.8 lb/ft3 in comfort layers. For memory foam, 4.0 lb/ft3 or higher indicates quality that will last. Lower density foams in either category will lose their support factor within a few years of regular use.
What Actually Matters for Sleep
Foam specifications are useful for comparing mattresses, but they do not tell the whole story. Here is what our team at Mattress Miracle focuses on when helping customers choose.
The Complete System Matters More Than One Layer
A mattress is a system. The Restonic ComfortCare Queen, for example, uses foam comfort layers over 1,222 individually wrapped coils. The foam provides surface comfort and pressure relief, while the coils handle deep support and airflow. Judging the mattress by its foam alone is like judging a car by its seats alone.
Dorothy often explains it this way: "The foam is what you feel first. The coils are what your back feels all night. You need both working together."
Your Sleep Position Changes the Equation
Side sleepers generally benefit from memory foam's conforming ability. It relieves pressure on the shoulder and hip. Back sleepers often do well with either type, as long as the support factor is adequate to maintain spinal alignment. Stomach sleepers usually prefer the firmer, more responsive feel of high-density poly-foam, which prevents excessive sinking.
Temperature Sensitivity
Traditional memory foam retains heat, which can be an issue for warm sleepers. Newer formulations use gel infusions, copper particles, or open-cell structures to improve airflow. Poly-foam generally breathes better out of the box. If you sleep warm, this is worth considering when choosing between the two.
Our Restonic Luxury Silk and Wool addresses this by using natural fibre layers over the foam for better temperature regulation. Wool and silk wick moisture and breathe naturally, complementing the foam system underneath.
Why You Should Test In Person
Support factor numbers are helpful for narrowing down options, but nothing replaces lying on the mattress yourself. Come to our Brantford showroom, spend 10-15 minutes on each model you are considering, and pay attention to how the foam responds to your body. The numbers confirm what you feel, but feeling is believing.
How to Test Foam Quality in a Showroom
You do not need a lab to assess foam quality. Here are some practical tests our team recommends.
The Press and Release Test
Press your hand firmly into the mattress surface and release. Poly-foam bounces back almost immediately. Memory foam holds the impression for a few seconds before slowly recovering. Neither response is better. It depends on your preference for responsiveness versus conforming.
The Sit and Stand Test
Sit on the edge of the mattress with your full weight. If the edge compresses dramatically and you feel like you might slide off, the foam layers lack adequate support factor. A well-made mattress maintains edge support even with concentrated weight.
The Roll Test
Lie in the centre of the mattress and roll from your back to your side. A mattress with good support factor will adjust to your new position without creating a deep valley where you were lying. If you feel trapped in a body impression, the foam's support factor may be too low for your weight.
Poly-foam or memory foam? Mattress Miracle at 441½ West Street in Brantford carries mattresses with both materials so you can feel the difference. Poly-foam bounces back faster and sleeps cooler. Memory foam contours more closely but can trap heat. The right choice depends on your sleep position and temperature preferences. Talia can walk you through the feel of each material on the showroom floor. Call (519) 770-0001.
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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 1997. Come try mattresses in person and get honest, no-pressure advice.
441 1/2 West Street, Brantford, Ontario
Call 519-770-0001Frequently Asked Questions
What is a good support factor for a mattress?
A support factor of 2.0 or higher is considered good for comfort layer foam. For long-term durability and deep compression support, look for 2.4 or above. Higher support factor means the foam progressively firms up as you press deeper, preventing bottoming out and maintaining comfort over years of use.
Is memory foam better than poly-foam?
Neither is universally better. Memory foam excels at pressure relief and motion isolation, making it ideal for side sleepers and couples. Poly-foam offers better breathability and a more responsive feel, which suits stomach sleepers and people who prefer to feel "on top of" rather than "in" the mattress. Quality and density matter more than foam type.
How long does foam last in a mattress?
High-density foam (1.8+ lb/ft3 for poly-foam, 4.0+ lb/ft3 for memory foam) typically maintains its properties for 7-10 years. Lower density foam may start losing support factor within 3-5 years. Rotating the mattress regularly and using a mattress protector helps extend foam life.
Can I try different foam types at Mattress Miracle?
Yes. Our Brantford showroom has mattresses featuring different foam technologies, including hybrid models with both foam and coil systems. Talia, our showroom specialist, can guide you through models with different foam types so you can compare the feel firsthand. Call (519) 770-0001 to schedule a visit.
Does body weight affect which foam type is better?
Yes. Heavier sleepers (over 230 pounds) generally need foam with a higher support factor to prevent excessive sinking. High-density memory foam or high-resilience poly-foam with support factors above 2.4 work well. Lighter sleepers (under 150 pounds) may find that lower support factor foams provide adequate comfort and pressure relief.
Sources
- Defloor, T. (2000). The effect of position and mattress on interface pressure. Journal of Clinical Nursing, 9(6), 827-835. doi.org/10.1046/j.1365-2702.2000.00423.x
- Jacobson, B.H., et al. (2008). Effect of prescribed sleep surfaces on back pain and sleep quality in patients with low back pain. Journal of Chiropractic Medicine, 7(1), 1-8. doi.org/10.1016/j.jcme.2007.11.003
- 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
- ASTM International. (2021). ASTM D3574 - Standard Test Methods for Flexible Cellular Materials. ASTM International Standards.
- Polyurethane Foam Association. (2019). In Touch Technical Bulletin: Flexible Polyurethane Foam. PFA Publications.
Visit Our Brantford Showroom
We are located at 441½ West Street in downtown Brantford. Free parking available. Our team does not work on commission, so you get honest advice based on your needs.
Mattress Miracle , 441½ West Street, Brantford, ON · (519) 770-0001
Hours: Monday–Wednesday 10am–6pm, Thursday–Friday 10am–7pm, Saturday 10am–5pm, Sunday 12pm–4pm.