IFD (Indentation Force Deflection) aka ILD (Indentation Load Deflection) is the method of determining the “softness” of foam by the flexible foam producers. IFD is obtained by measuring the pounds of pressure required to indent a four-inch piece of memory foam by 25%. The pressure is applied over a 50-square-inch area to conduct this test. The requisite pressure is then translated into a weight. This weight indicates the IFD seen on mattresses found in the market.
What are the Factors Affecting IFD?
The IFD rating is frequently given as a range, such as 10–12, rather than as a single number. This is due to the factors affecting a foam’s conditioning or the environment in which it was stored before testing.
Common factors that influence the IFD rating are:
- The thickness of the material
- Temperature and humidity
- The type of foam
- The manufacturer itself
How to Measure IFD?
An indentation penetrometer is used to measure IFD. This device compresses a foam that is 4-inch thick with a 15 x 15 surface area. Prior to testing, the foam is placed on the penetrometer’s perforated base which lets air escape during the compression process. The foam is then warmed, compressing it to 25% of its original thickness. The resulting force needed to compress this foam is noted down. After which the foam is compressed once again by 25-75% of its natural thickness. The last step compresses the foam to 65% of its starting thickness and after a minute, the resulting number is recorded as the IFD rating.
What do IFD Ratings Represent?
IFD provides for an objective and standard measure to evaluate the foam thickness of mattresses. The following summarizes IFD ratings and correlates them to a mattress’ firmness:
- Extra plush- less than 16.5 lbs
- Plush- 16.5-22.5 lbs
- Soft- 22.5-26.5 lbs
- Medium- 25.6-30.5 lbs
- Firm- 30.5-34.5 lbs
- Extra -firm- 34.5-38.5 lbs
