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ILD + Density

As you may know, we use two densities of latex in our mattresses: Medium and Firm. Please note that there isn't an ILD for the mattress, but an ILD for each individual layer of latex.

Chart of ILD and Density of Spindle's medium and firm layers

Please note that we do not use a soft layer of latex. With our design using three, three-inch layers of latex, we found it to not perform well for most people. In other applications, a soft layer can be a good option. We have reconfigured our Soft mattress so that it can accommodate a wider range of body types. And, it's still relatively soft.

Chartof the configurations for Spindle's soft, medium, firm, and extra firm mattresses

Many people try to use Indentation Load Deflection, commonly known as ILD, as a metric when trying to decide which mattress to buy. We are happy to share our ILD data with you, but we also caution you not to base your decision on that number alone. ILD is only accurate when comparing the same type of latex from the same latex manufacturer. So, if you are doing a comparative analysis, we suggest you use the lower limit of the tolerance at the 40% compression rating when comparing our latex to Talalay. As for molded Dunlop from Sri Lanka or India, it’s important to look at the ILD in conjunction with the density. This is one of the reasons why we prefer to not publicly display the ILD as a marketing tool — because you need a decoder ring and a flashlight, and without it you may select the wrong firmness.

Another complication is our latex manufacturer also makes a blended latex with a lower density, but with the same ILD. If you tried comparing one mattress made of a blended latex and another one made with 100% natural latex using the same ILDs, the two mattresses would feel completely different.

And then, it turns out equivalent ILDs from the two Talalay producers, Latex International and Radium, don’t ultimately produce the same feel. We’ve only dealt with Radium and they are not sure why the numbers don’t match up feel-wise. Their thought is there is a difference in the way that LI measures the ILD, but they aren’t totally sure. All we know for sure is you can’t make a direct comparison based on ILD for Talalay, which isn’t used in our mattresses.

We know it would be easier if there was one unified number, but feel is ultimately subjective and based on more than a single input test like ILD.

We'd caution against using ILD alone to make a direct comparison especially with something as subjective as comfort. Like going to buy a pair of sneakers, a size 12 in a Nike isn't the same in New Balance or any other company. In fact, we made a video about the differences of ILD.

There a lot of other factors beyond ILD that affect the feel like thickness of the latex, density, pinhole diameter, etc. and there are other factors beyond the latex alone that affect the feel of the mattress like the type of fabric, quilt pattern, tightness/looseness of the cover, etc. We could two design a mattress using identical latex and make one feel a lot firmer just by changing the cover.

 

Keep in mind that firmness is totally subjective. One person's firm and can be another one's soft. For example, we did a focus group and put ten people in a room to test out the medium, five may said it is medium, two said it is soft, two said firm, and one thought it is extra firm. It depends on the person's past experiences, height, weight, and sleep position. This is where in store testing may be helpful because it helps us come to closer idea of what is soft, medium, and firm, but it isn't foolproof.