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Exploring ILD

Plastic toy numbers in a pile

Update: Most latex suppliers no longer provide ILD (Indentation Load Deflection) measurements for their products. ILD is a technical specification some people are curious about, however. This post discusses the limitations of this approach in choosing natural latex for your mattress.

ILD (indentation load deflection), also called IFD (indentation force deflection) is a measurement of the force required to compress a material by 25% of its thickness. While ILD can be a helpful technical tool for characterizing a sheet or layer of latex, it is often misused or misunderstood.

At Savvy Rest, we recommend customized layer configurations for mattresses based on years of experience, customer interviews and customer feedback, not ILDs.

Now and then, though, we’ll field a question about latex ILDs and how they relate to mattress comfort. In order to provide a more complete understanding, we purchased an ILD tester and did some research ourselves.

Here are some of the things we found out:

  1. The instrument used to measure ILD is a 7.5” diameter circular plate, shaped nothing like a person. So, ILD measurements can’t be applied directly to how the foam interacts with your sleeping body.
  2. The ILD rating is valid at 25% compression only. It does not indicate how foam performs when it is compressed more or less than that. For example, some of our Dunlop latex pieces have ILDs similar to our Talalay pieces. The Dunlop piece will typically feel firmer, however. That’s because when Dunlop is compressed by more than 25%, it “firms up” more than Talalay does. 
  3. One part of your body (your hips, for example) will compress latex more than another part (such as your feet), and no sleeper’s entire body would compress a layer at exactly 25%.
  4. Sheets of latex foam will not have the exact same ILD across the entire sheet. The stated ILD for a layer represents the average of multiple measurements, but the variations are undetectable to a sleeper.
  5. Actual ILD measurements depend on the thickness of the latex. For example, a 6” sheet of latex with an ILD of 22, when cut in half, will result in two 3” sheets with ILDs of 13 – 15. Based on our test results this applies to all latex made by all manufacturers, using either the Dunlop or Talalay process.
  6. ILD is only one factor that characterizes how soft or firm a piece of latex is.

The construction of a mattress casing (sometimes called quilting or ticking) also makes a difference in the surface feel by adding cushioning. If a casing is constructed to fit very tightly, the taut surface and compression add to a sensation of firmness. On the other hand, if a casing or quilting is made with lots of fiber or loft and with very stretchy fabric, it can be made to feel very soft right out of the factory.

Identifying the right mattress firmness for your body isn’t hard. The best option is to try our mattress—with different configurations—at the nearest Savvy Rest dealer. If there’s no dealer within reach, call Savvy Rest and talk with us about how the mattress will feel. We’ll ask you guided questions that will help you swiftly make sense of it.

The bottom line on ILD? Your sleep experience depends on much more than the ILD measurements of individual layers—so don’t let the numbers keep you up at night.

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