Quick Answer: Compression modulus (also called support factor or ILD ratio) measures how much a latex material stiffens as it compresses deeper. A high compression modulus means the latex provides gentle initial contact but firms up significantly before bottoming out - the ideal for joint support. ILD (Indentation Load Deflection) measures firmness at a specific depth, while compression modulus describes behaviour across the full compression range. Both numbers matter for evaluating a latex mattress.
In This Article
Reading Time: 9 minutesWhat Is Compression Modulus?
In materials science, modulus describes the relationship between stress (applied force per unit area) and strain (deformation). For a mattress material, compression modulus describes how the resistance to compression changes as the material is pressed further down.
A material with a low compression modulus compresses at roughly the same rate throughout its depth - push it 25 percent of its thickness or 65 percent of its thickness, and the resistance increases proportionally. A material with a high compression modulus has a non-linear response: it feels relatively soft in the first 25 to 30 percent of compression, then firms up significantly as compression increases further.
For a mattress, high compression modulus is generally desirable. It allows the surface to feel soft and pressure-relieving against the body's lighter-load areas (shoulders, ankles, knees) while becoming firm enough to support the heavier areas (hips, lower back) before they sink too deep. Low compression modulus materials feel uniformly soft throughout and can bottom out under heavier body zones, losing support precisely where it is most needed.
Why Support Without Bottoming Out Matters
When the heaviest body zone - typically the hips in side sleepers - sinks past the support zone of a mattress, the spine drops into a curved position that is not maintained through the full sleep cycle. Research on spinal alignment during sleep (Leilnahari et al., 2011) found that lateral sleep posture with proper hip support maintained significantly better spinal alignment than postures where the hip sank below the shoulder line. A high-modulus material prevents this hip-below-shoulder scenario by firming up under increased load before the sleeper reaches a misaligned position.
ILD and IFD: What These Ratings Mean
ILD (Indentation Load Deflection) and IFD (Indentation Force Deflection) are two names for essentially the same measurement. The test applies a circular plate to a foam or latex sample and measures the force required to compress the material to 25 percent of its thickness. The result is expressed in pounds.
Standard ILD ranges for latex:
- Under 20 ILD: Very soft. Suitable for lightweight sleepers or as a top comfort layer only.
- 20 to 28 ILD: Soft to medium-soft. Common in comfort layers for side sleepers.
- 28 to 36 ILD: Medium to medium-firm. The most versatile range; suitable for most adult body types in a comfort position.
- 36 to 44 ILD: Firm. Appropriate for support cores, heavier sleepers, or stomach sleepers.
- Above 44 ILD: Very firm. Used in support cores or perimeter edge reinforcement.
The critical limitation of ILD as a specification: it only describes resistance at one compression depth (25 percent). It tells you nothing about how the material behaves at 40, 50, or 60 percent compression - which is exactly where the heaviest body zones operate in a sleeping position. This is why compression modulus and support factor data are more informative than ILD alone.
Support Factor: The Number That Actually Matters
Support factor (also written as "compression modulus" or "sag factor" in older literature) is calculated by dividing the ILD at 65 percent compression by the ILD at 25 percent compression.
Example: A latex sample that requires 25 lbs to compress 25 percent and 75 lbs to compress 65 percent has a support factor of 75/25 = 3.0.
Good support factor ranges for latex:
- Below 2.0: Low support factor. The material barely stiffens with deeper compression. Not ideal for heavier body zones.
- 2.0 to 2.5: Adequate. Suitable for lighter sleepers or as an upper comfort layer.
- 2.5 to 3.0: Good. The most common range for quality Talalay latex.
- 3.0 to 4.0: Excellent. Typical of quality Dunlop latex and high-density Talalay. Best for heavier sleepers or anyone needing robust joint support.
A latex mattress or layer with an ILD of 24 (soft initial feel) and a support factor of 3.2 provides a surface that feels soft on initial contact but resists bottoming out under heavier loads. This combination is difficult to replicate with foam, which typically has support factors of 1.5 to 2.2 even in high-quality formulations.
Dunlop vs Talalay: Modulus Differences
The two primary latex manufacturing processes produce different compression modulus profiles:
Dunlop Process
Liquid latex is poured into a mould and vulcanised. During the process, heavier particles settle toward the bottom before vulcanisation is complete, creating a natural density gradient - the bottom of a Dunlop layer is denser and firmer than the top. Dunlop latex typically has a higher support factor (3.0 to 4.0) than Talalay at the same ILD.
This makes Dunlop particularly appropriate for support cores in latex mattresses. The inherent density gradient means it provides a progressive resistance that increases meaningfully with deeper compression.
Talalay Process
Liquid latex is poured into a mould that is only partially filled, vacuum-expanded to fill the mould, then flash-frozen before vulcanisation. This process creates a more uniform open-cell structure throughout the material. Talalay latex at the same ILD rating as Dunlop has a lower support factor (2.5 to 3.0 typically) but a more consistent feel throughout its depth.
This consistency makes Talalay well-suited for comfort layers where a predictable, even feel is desired. The flash-freeze process also creates the pinhole structure that gives Talalay superior airflow compared to Dunlop.
Dunlop vs Talalay: The Practical Difference We Explain In-Store
Brad explains the difference with a simple test when customers visit: press into the mattress with one finger vs your full palm. Talalay feels similar with both. Dunlop firms up more noticeably with the full palm because it distributes load more broadly and hits the high-density lower zone. Neither is better in the abstract - Talalay for comfort layers, Dunlop for support cores, is the general rule we follow for most customers. But body weight changes the calculation. Heavier sleepers often benefit from Dunlop in the comfort layer as well because it resists bottoming out more effectively.
Natural vs Synthetic Latex
Natural latex comes from the Hevea brasiliensis rubber tree. Synthetic latex (Styrene-Butadiene Rubber, or SBR) is petroleum-derived. Blended latex combines both.
For compression modulus purposes:
- Natural latex generally has superior resilience (bounce-back speed after compression) and a higher support factor than SBR at equivalent densities.
- Synthetic latex has a more linear compression response (lower support factor) and loses resilience faster over time.
- Blended latex varies depending on the ratio; most blends use 30 to 70 percent natural latex.
GOLS (Global Organic Latex Standard) certification indicates a latex product is at least 95 percent organic natural latex. OEKO-TEX Standard 100 certification indicates testing for chemical substances of concern. These certifications are meaningful and relevant when evaluating the material claims of any latex mattress.
Choosing Latex for Your Body Type
| Body Weight | Sleep Position | Recommended Comfort Layer ILD | Recommended Support Factor |
|---|---|---|---|
| Under 130 lbs | Side | 18 to 24 ILD | 2.5+ |
| Under 130 lbs | Back/Stomach | 24 to 32 ILD | 2.5+ |
| 130 to 200 lbs | Side | 22 to 28 ILD | 2.8+ |
| 130 to 200 lbs | Back/Stomach | 28 to 36 ILD | 3.0+ |
| 200 to 250 lbs | Side | 28 to 36 ILD | 3.2+ |
| 200 to 250 lbs | Back/Stomach | 36 to 44 ILD | 3.5+ |
| Over 250 lbs | Any | 36 to 44 ILD | 3.5+ |
Latex in the Revive Lineup
The Revive Tiffany Rose and Revive Jasmine (both $1,995) use Talalay copper latex as the primary comfort material. Copper-infused Talalay maintains the open pin-hole structure of standard Talalay (for airflow) while adding thermal conductivity through the copper particles. The ILD and support factor of these models sits in the medium range appropriate for most adult body types in a side or back sleeping position.
The Revive St Charles ($2,150) uses a layered latex construction with different ILD zones through the depth of the mattress, creating a built-in compression modulus profile rather than relying on a uniform block. This approach gets closer to the ideal progression described in the support factor discussion above: softer at the surface where pressure relief is most important, firmer at depth where spinal support matters most.
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Call 519-770-0001Frequently Asked Questions
What ILD should I choose for a latex mattress?
ILD should be matched to your body weight and sleep position, but it only tells part of the story. A 24 ILD latex with a 3.2 support factor performs very differently from a 24 ILD latex with a 2.0 support factor. If you are evaluating a latex mattress, ask for both the ILD and the support factor (or compression modulus) for the comfort layer. The support factor matters as much as the ILD number for most sleepers above 150 lbs.
Does latex soften over time?
Natural latex retains its resilience for considerably longer than polyurethane foam. Some softening occurs in the first few weeks as the material settles, but quality natural latex - particularly Dunlop - typically loses only 10 to 15 percent of its original ILD value over 10 years of normal use. Synthetic latex and low-grade blends can soften significantly faster. Flipping or rotating a latex mattress helps distribute wear evenly.
Is latex appropriate for people with latex allergies?
Natural latex contains proteins (specifically Hevea proteins) that can trigger reactions in people with latex sensitivity. Most reactions require direct skin contact with the latex over extended periods. A latex mattress with a full mattress cover, mattress protector, and fitted sheet creates sufficient barrier for most people with mild sensitivity. For those with documented latex allergy (anaphylactic response), a latex mattress is not recommended. Synthetic SBR latex does not contain Hevea proteins and is generally safe for people with natural rubber latex allergy.
Can I use a latex topper to change the feel of my current mattress?
Yes, and this is one of the most cost-effective ways to add compression modulus to an existing mattress that bottoms out under heavier loads. A 2-inch Dunlop latex topper at 36 to 40 ILD placed on top of a softer mattress adds a high-support-factor layer that resists the hip-sinking problem. It will make the overall surface firmer, so it works best on mattresses that are currently too soft rather than too firm.
What is the difference between compression modulus and ILD for shopping purposes?
ILD tells you how the surface feels when you first lie down. Compression modulus (support factor) tells you whether the material will support you properly once your body weight has pressed into the comfort layer. Both numbers matter. If a manufacturer only provides ILD, ask specifically for the support factor or compression ratio. Reputable latex manufacturers publish both for each product.
Sources
- Leilnahari K, Fatouraee N, Khodadadeh S, Amiri A, Naserkhaki S. (2011). Spine alignment in men during lateral sleep position: experimental study and modeling. Biomedical Engineering Online, 10(1), 103.
- Jacobson BH, Gemmell HA, Hayes BM, Altena TS. (2008). Grouped comparisons of sleep quality for new and personal bedding systems. Applied Ergonomics, 39(2), 247-254.
- Defloor T. (2000). The effect of position and mattress on interface pressure. Applied Nursing Research, 13(1), 2-11.
- Chadwick EK, Nicol AC, Murray PA. (2014). Musculoskeletal loading conditions at the shoulder during sleeping positions. Manual Therapy, 19(4), 289-293.
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