What Is Indentation Force Deflection (IFD) in Canadian Foam Mattresses?

Most mattress shoppers in Canada have heard terms like "medium-firm" or "plush" without any real definition behind them. One company's "medium" feels completely different from another's, which makes comparing mattresses almost impossible online or even in a showroom without knowing the underlying numbers.

IFD solves that problem. It is an objective, lab-measured number that describes how much force is needed to compress a foam layer to a defined depth. Once you understand IFD, you can compare mattresses from different manufacturers on equal terms, ask the right questions in a showroom, and make a purchasing decision that is based on data rather than marketing language.

This guide explains what IFD is, how it is measured, and how to use it to find the right mattress for your body weight and sleep position.

What IFD Actually Measures

IFD stands for Indentation Force Deflection. Some manufacturers and foam suppliers use the older term ILD (Indentation Load Deflection), but both terms describe the same measurement using the same test standard. The two terms are interchangeable.

In simple terms, IFD measures how many pounds of force you need to press a circular indenter into a foam sample and compress it by exactly 25 per cent of its original thickness. A foam block that is 100 mm thick will be compressed to 75 mm during the test. The amount of force required at that point of compression, measured in pounds, becomes the IFD rating.

The test is performed on a standardised foam sample under controlled temperature and humidity conditions. The indenter has a specific surface area (323 square centimetres, or roughly 50 square inches), and the foam must be conditioned before testing. These controls ensure that results are repeatable and comparable across different labs and manufacturers.

A foam with an IFD of 15 requires only 15 pounds of force to compress it 25 per cent. That foam would feel very soft under your body. A foam with an IFD of 45 requires 45 pounds, and would feel quite firm. The number scales directly with perceived firmness when all other variables are equal.

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How IFD Is Tested (ASTM D3574)

The governing test standard for IFD in North America is ASTM D3574, published by ASTM International (formerly the American Society for Testing and Materials). This standard is used by foam manufacturers and certification bodies across Canada and the United States.

The ASTM D3574 test procedure for IFD includes the following steps:

• Sample preparation: A foam sample is cut to at least 380 mm x 380 mm and 100 mm thick. The sample must be conditioned at 23°C and 50 per cent relative humidity for at least 16 hours before testing.
• Pre-flex: The sample is compressed to 75 per cent of its original thickness three times to eliminate the first-compression effect (foam is always softer on its first compression). This step ensures that the IFD number reflects real-world, in-use firmness rather than brand-new feel.
• Indenter contact: A circular, flat-faced indenter with a surface area of 323 cm² is centred on the foam sample. It descends at a controlled rate of 50 ± 5 mm per minute.
• Force measurement at 25 per cent: When the indenter has compressed the foam by 25 per cent of the sample thickness (25 mm for a 100 mm sample), the force in pounds is recorded. This is the IFD rating.
• Optional 65 per cent measurement: The indenter continues compressing to 65 per cent depth and the force is recorded again. This second number is used to calculate the support factor (see below).

Because the test pre-flexes the foam to eliminate first-compression effects, ASTM D3574 IFD numbers reflect how the foam performs after you have slept on it a few nights, not how it feels when it is factory-fresh. This makes it a reliable predictor of long-term comfort.

IFD Rating Chart for Canadian Buyers

The following chart shows how IFD ratings correspond to perceived firmness in mattress comfort layers. These ranges apply to polyurethane foam and memory foam. Latex IFD ratings behave somewhat differently because latex has a higher support factor (it gets firmer faster as compression increases).

Keep in mind that the comfort layer IFD is what you feel when you first lie down. The support core (typically high-density foam or coils) determines how well the mattress maintains spinal alignment over time. A mattress with a very soft comfort layer (IFD 15) over a firm support core (IFD 40+) can provide both pressure relief and adequate support.

IFD vs. Foam Density: Two Different Things

IFD and foam density are the two most important specifications for evaluating foam quality, and they measure completely different properties. Many buyers confuse them or assume they are related.

IFD measures firmness (how soft or hard the foam feels). It tells you nothing about how long the foam will last or how well it will hold up after years of use.

Density measures durability (how much foam is packed into a given volume). Density is expressed in kilograms per cubic metre (kg/m³) or pounds per cubic foot (PCF). A 4-PCF foam contains more raw material per unit of volume than a 2-PCF foam, and will generally last longer before breaking down and developing body impressions.

You can have a high-IFD (firm) foam with low density, meaning it will feel firm at first but wear out quickly. You can also have a low-IFD (soft) foam with high density, meaning it will feel plush but hold up well over time. The ideal mattress has both appropriate IFD for your sleep position and adequate density for long-term durability.

When evaluating any mattress, ask for both the IFD and the density of each foam layer. A manufacturer that cannot or will not provide both numbers is one worth approaching with caution.

Support Factor: The Number Brands Hide

The support factor (sometimes called the sag factor or comfort factor) is a derived measurement from the ASTM D3574 test that tells you how a foam transitions from light to heavy compression. It is calculated by dividing the 65 per cent IFD reading by the 25 per cent IFD reading.

A foam with an IFD of 30 at 25 per cent compression and an IFD of 90 at 65 per cent compression has a support factor of 3.0. That foam feels relatively soft when you first press on it but gets significantly firmer as you sink deeper. This type of foam provides a feeling of being "cradled" by the mattress without the sensation of bottoming out.

A support factor below 2.0 means the foam firms up slowly and may allow excessive sinking. A support factor above 2.5 means the foam provides progressive resistance, which most sleep specialists consider ideal for spinal alignment during sleep.

Which IFD Is Right for Your Sleep Position?

IFD preferences are not purely subjective. Sleep position, body weight, and health conditions all influence the optimal IFD for the comfort layers and support core of your mattress.

Side Sleepers

Side sleeping concentrates body weight on the shoulder and hip. These joints need to sink into the mattress to allow the spine to remain straight. Comfort layers in the 15-28 IFD range generally work best for side sleepers. Heavier side sleepers (over 180 lbs) may prefer the upper end of that range or a 28-32 IFD layer to avoid bottoming out, while lighter sleepers tend to do better with softer comfort layers.

Back Sleepers

Back sleeping distributes weight more evenly across the lumbar spine. The lower back needs support without the mattress pushing up against its natural curve. Comfort layers in the 28-36 IFD range paired with a firm support core (40-50 IFD) typically provide the right balance. Most clinical guidelines on sleep and low back pain recommend medium-firm surfaces for back sleepers.

Stomach Sleepers

Stomach sleeping can strain the lumbar spine if the midsection sinks too deeply into the mattress, causing the spine to hyperextend. Stomach sleepers generally need firmer surfaces, with comfort layer IFD in the 35-45 range. Very soft comfort layers increase the risk of lower back pain for this sleep position.

Combination Sleepers

Combination sleepers shift between positions throughout the night. A medium IFD comfort layer (28-35) that responds to position changes without excessive resistance tends to work best. This profile also suits couples with different sleep positions sharing the same mattress.

IFD and Canadian Foam Certifications

In Canada, foam mattresses that carry CertiPUR-US certification have been tested by an independent laboratory for both content (no harmful chemicals) and physical properties. The CertiPUR-US standard requires foam to meet minimum performance thresholds, and IFD is among the properties that are independently verified.

When you see a CertiPUR-US seal on a mattress, the foam inside has been tested at an accredited laboratory using ASTM D3574 or equivalent methods, and the IFD values on the product spec sheet should match the lab results within a defined tolerance. This gives Canadian buyers confidence that the IFD number listed is real, not a marketing approximation.

Greenguard Gold certification, which some premium Canadian mattress brands carry, primarily covers off-gassing of volatile organic compounds (VOCs) rather than mechanical foam properties, so it does not directly verify IFD.

For latex mattresses, the equivalent standard is ASTM D3574 combined with GOLS (Global Organic Latex Standard) certification for organic latex content. Latex IFD values are measured the same way as polyurethane foam IFD values, but latex typically has a higher support factor, meaning it feels firmer under heavier compression even when the 25 per cent IFD number appears similar to a polyurethane foam.

How Mattress Miracle Uses IFD Ratings

Family-owned since 1997, Mattress Miracle has spent nearly four decades learning what makes a mattress last. One of the clearest lessons from that time is that customers who understand IFD make better decisions and return fewer mattresses.

When Dorothy walks a customer through our Restonic lineup, she always checks their body weight and sleep position before directing them to a firmness profile. The Restonic HealthRest and Comfort Care lines include models with clearly documented comfort layer IFD values, and our team uses those numbers to match each customer to the right feel.

We also advise customers on the relationship between IFD and mattress longevity. A comfort layer with the right IFD for your body weight will experience less compression fatigue over time, because the foam is not being pushed beyond its optimal working range every night. Choosing a foam that is too soft for your weight accelerates body impression development. Choosing one that is too firm increases pressure-point discomfort and reduces sleep quality.

If you have purchased a mattress elsewhere and are uncertain whether the IFD is appropriate for you, visit our showroom. We do not charge a consultation fee and are happy to help you diagnose whether your current mattress is right for your sleep needs or whether an adjustment is warranted.

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