Many shoppers looking for a memory foam mattress believe firmness is the same thing as density. But they are 2 very different things and are not directly related. Foam firmness is straight forward; it's how hard or soft the foam is. Foam density is only a little more difficult to conceptualize. It is a measure of weight and volume that tells you how much material is in 1 cubic foot of foam. High density foam will last longer and is more expensive than low density foam, but can be either firm or soft.
Foam bed firmness is measured in a lab by pushing a rigid, flat surface into the surface of foam. The units of measurement are expressed as a numerical value of Indentation Force Deflection (IFD). IFD is defined as a measure of the load bearing capacity of flexible polyurethane foam. IFD is generally measured as the force (in pounds) required to compress a 50 square inch circular indentor foot into a 4 inch thick sample, typically 15 inches square or larger, to a stated percentage of the sample's initial height. Initial Load Deflection (ILD) is another term meaning the same thing.
Lower IFD = softer foam
Higher IFD = firmer foam
Common values for the top layer of a memory foam mattress range from 12 - 15 IFD. Foam bed base layers typically range from 20 - 40 IFD
Foam Bed Firmness versus Support
Firmness is not the same thing as support. Good foam beds should be both soft and supportive, but some bad mattresses are both too firm and offer little support. The most common IFD value
measures indentation to 25% of the total height of a piece of foam. This is called 25 IFD and tells us how soft or firm the surface of a particular foam feels. If a retailer can give you an IFD, this is the value he will give you.
While you want a foam bed to softly contour to your body, you don't want it to completely compress or "bottom out." Good foam does two things; it contours and supports. Support is determined by taking measurements deeper into the foam and is called support factor. Support factor is important for telling mattress makers how much weight a memory foam layer will optimally support.
Firmness and Flex Fatigue
Flex fatigue is the normal softening of foam beds with use and over time. You can expect your mattress to get 5-15% softer by the end of its useful life. Higher density foams (3 lbs and up) hold their original firmness best. In general, the higher the density, the better it will retain its firmness.
Be Aware of Firmness and Support When Shopping
IFD values are generally not available from your retailer, and they would not help you decide which bed is for you anyway. Often IFD values are different from one manufacturer to the next, but feel very similar. They are not a good way to compare mattresses. But understanding IFD will help you be aware of comfort and support when mattress shopping.
When testing mattresses, be aware of how soft or firm the bed feels when you first lay down. Then think about how the bed supports your lower back and neck. Is there an even pressure applied across the surface of your body, or is there most pressure on your hips and shoulders? Regardless of firmness, a memory foam mattress should conform to your body and reduce pressure points.
Foam bed firmness is measured in a lab by pushing a rigid, flat surface into the surface of foam. The units of measurement are expressed as a numerical value of Indentation Force Deflection (IFD). IFD is defined as a measure of the load bearing capacity of flexible polyurethane foam. IFD is generally measured as the force (in pounds) required to compress a 50 square inch circular indentor foot into a 4 inch thick sample, typically 15 inches square or larger, to a stated percentage of the sample's initial height. Initial Load Deflection (ILD) is another term meaning the same thing.
Lower IFD = softer foam
Higher IFD = firmer foam
Common values for the top layer of a memory foam mattress range from 12 - 15 IFD. Foam bed base layers typically range from 20 - 40 IFD
Foam Bed Firmness versus Support
Firmness is not the same thing as support. Good foam beds should be both soft and supportive, but some bad mattresses are both too firm and offer little support. The most common IFD value
measures indentation to 25% of the total height of a piece of foam. This is called 25 IFD and tells us how soft or firm the surface of a particular foam feels. If a retailer can give you an IFD, this is the value he will give you.
While you want a foam bed to softly contour to your body, you don't want it to completely compress or "bottom out." Good foam does two things; it contours and supports. Support is determined by taking measurements deeper into the foam and is called support factor. Support factor is important for telling mattress makers how much weight a memory foam layer will optimally support.
Firmness and Flex Fatigue
Flex fatigue is the normal softening of foam beds with use and over time. You can expect your mattress to get 5-15% softer by the end of its useful life. Higher density foams (3 lbs and up) hold their original firmness best. In general, the higher the density, the better it will retain its firmness.
Be Aware of Firmness and Support When Shopping
IFD values are generally not available from your retailer, and they would not help you decide which bed is for you anyway. Often IFD values are different from one manufacturer to the next, but feel very similar. They are not a good way to compare mattresses. But understanding IFD will help you be aware of comfort and support when mattress shopping.
When testing mattresses, be aware of how soft or firm the bed feels when you first lay down. Then think about how the bed supports your lower back and neck. Is there an even pressure applied across the surface of your body, or is there most pressure on your hips and shoulders? Regardless of firmness, a memory foam mattress should conform to your body and reduce pressure points.
Will Robertson is owner of MyLuxuryMattress.com, a specialty sleep shop featuring latex and memory foam mattresses, and luxury bedding including: down comforters & pillows, Egyptian cotton bed sheet sets & duvet covers, quilts, memory foam pillows, and bedding ensembles. Will answers his customers frequently asked luxury bedding questions at MyLuxuryMattress.com/Blog
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