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This standard replaced ILD as a measure of firmness in polyfoam and is almost identical with a different name. It pre-compresses a material with 1 lb of weight to make up for surface variations and is a little bit more accurate ... although for all intents and purposes they are interchangeable. We mostly use ILD on this website since it is more commonly known although is is not as "up to date" in the world of polyfoam at least.

Stands for Indentation Load Deflection. Usually used with latex as a measure of firmness but has been replaced with IFD in other foam types. It indicates the amount of force it takes to compress a layer of foam by specific percentage of its depth. The most common form uses a 50 sq in deflector foot to depress a 20" x 20" layer of material that is 4" thick by 25% of its height. There are also versions however that use 6" of material (most latex for example) or a greater or lesser percentage of compression (many European or Asian manufacturers use 40% instead of 25%) all of which give different results so ILD ratings are not always comparable between different materials.
An layer of interconnected wire coils of differing properties and number that is used as a support layer in a mattress. They come in different types and with many variations in both performance and quality. They are the most widely used support layer in a mattress.
Insulator Layer
A layer that used over an innerspring to both protect the layers above it and prevent them from sinking into the coils and to adjust the properties and feel of the innerspring. There are many different types of insulator materials and methods of using them and while they are little known, they can have a major effect on the feel and qualities of an innerspring and mattress.
Insulator Layer
This is a layer which is used over an innerspring to prevent the layers above it from shifting into the innerspring and is also used to alter the feel or response of the innerspring itself.

The more subjective qualities of a mattress based on a "feeling" without necessarily affecting the pressure relief or support qualities (or other "measurable qualities) of a mattress.