Latex Firmness (ILD) and Your Sleep Experience

What is ILD?

ILD, or Impression Load Deflection, is a measure of the softness or firmness of a foam mattress. ILD is measured by pressing a 12-inch round disk into a 4-inch piece of foam until it presses 25% or one inch into the mattress surface. The amount of weight or pressure required to compress the mattress to that extent is the ILD.

ILD is sometimes referred to by the alternate name IFD, or Impression Force Deflection. The terms ‘ILD' and ‘IFD' are interchangeable. Both measure the force it takes to compress a foam latex mattress by a measurable amount.

ILD and Density

With latex, "there's a straight-line relationship between ILD and density", according to Lynn Holt, latex expert. In other words, denser mattresses are firmer and thus have a higher ILD, while less dense mattresses tend to be less firm and thus have a lower ILD.

In the foam mattress industry, the standard "density" measurement is translated as the weight of a 12 inch x 12 inch x 12 inch block of a particular foam. A higher density measure corresponds to a higher ILD.

Are All Foam Mattresses the Same?

If all foam mattresses are measured using ILD or density, does that mean all foam mattresses are the same? Some companies would have you believe so, but natural botanical latex possesses properties that synthetic materials, even those with a similar ILD, simply do not have.

Botanical latex mattresses have a much quicker recovery time than memory foam. Memory foam very slowly regains its shape, while latex springs back immediately. Latex foam actually bounces – the same properties that make a rubber ball bouncy apply to the foam as well. The same doesn't hold true for memory foam.

In addition, memory foam is very reactive to temperature. Higher temperatures can actually reduce the ILD of memory foam so that it is softer and less supportive. Since memory foam tends to "sleep hot," holding onto your body temperature, the contact of your body with the mattress over the course of the night can actually cause you to begin to sink into the bed within a few hours of falling asleep.

A similar ILD shared by a memory foam mattress and a botanical latex mattress does not, therefore, mean that memory foam is a product on par with natural latex.

Lower ILD vs. Higher ILD

An important latex faq for choosing a mattress firmness: The lower the ILD rating, the softer the mattress. The higher the ILD rating, the firmer the mattress. Quantitative ILD measurements have been divided into ranges that correspond to qualitative descriptions of soft, medium, medium-firm, and firm. Typically there is allowed a few points of "wiggle room" between each designation. If the mattress you're looking at is a 22, for instance, it will fall into the space between a "soft" and a "medium" foam mattress.

Soft to Medium Latex

A "soft" mattress is one that is so soft that only those who prefer to sink into their mattress will be pleased with the support. The "soft" designation corresponds to an ILD rating of 19-21.

A "medium" foam mattress is an excellent "middle of the road" mattress that blends support with softness, and tends to be a highly popular mattress among side sleepers. The ILD rating for the medium range is 24-26.

In general, because of the distinctive processing techniques, the more aerated Talalay latex tends to be softer than the firmer Dunlop latex, which contains a higher ratio of foam to air.

Medium-Firm to Firm Latex

"Medium-firm" foam mattresses fall into a range of 29-31 ILD. These mattresses are appealing to a wide range of back and stomach sleepers who prefer firm support that still allows enough "give" for a sense of comfort.

A "firm" foam mattress is so firm that few sleepers will find it truly comfortable, but for some back or stomach sleepers this level of support fits the bill. The ILD on firm mattresses ranges from 34-36.

Because of the natural differences in Talalay and Dunlop production methods, Dunlop latex mattresses tend to be firmer than their Talalay counterparts.