Glossary
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Glossary

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Glossaries

Term Definition
Adjustable Base

A mattress support system that is either tension adjustable, height adjustable, or position adjustable. The most common of the adjustable bases is an adjustable bed that can raise and lower the legs and torso either for leisure activities such as reading or watching TV or for health reasons such as snoring, acid reflux, pressure relief, or circulation.

Base

A generic term to describe any platform or other support system meant to support a mattress or increase the height of the sleeping surface. There are many types including boxsprings, slatted bases, wire grid bases, bunkie boards, foundations, platform beds, solid surface bases, and many others.

Body Impression

The permanent impressions in a mattress that often develop after repeated use over time. It is called a body impression as it forms in the shape of your body with the deeper impressions usually under the heavier areas. With natural fibers used in a comfort layer, it is an expected and desirable process as it is part of how these materials form a cradle and relieve pressure. With foam materials it indicates foam breakdown and the permanent loss of some of the foam's properties. Synthetic fibers like polyester used in comfort and quilting layers can also make a significant contribution to body impressions as they compact and become firmer over time.

Boxspring

Similar to an innerspring except it generally uses fewer and stronger coils or torsion springs and is used under an innerspring mattress to support it, protect it from sudden shocks that can damage the innerspring, and to help it's its ability to respond to weight and provide additional pressure relief or improve alignment. Some innerspring mattresses are made to work with specific boxsprings as part of their design.

Breathability

The ability of a material to allow air to flow through it. This is an important part of sleeping comfort and temperature regulation. Foams that have cells that are less open are also less breathable.

Comfort

A subjective feeling that is the result of many interacting factors. While it is often used to mean pressure relief, this can be misleading. The most important parts of the perception of comfort are ILD, support factor, resilience, hysteresis, hand feel (surface compression), point elasticity, pressure relief, and spinal alignment.

Comfort factor

Another term for Support Factor.

Compression Modulus

Another term for support factor.

Density

The weight per cubic foot (in imperial measurement)of a foam. With some types of foam such as polyfoam and memory foam, density is an important part of quality. Comparing different types of foam with different densities in terms of quality is meaningless. Good Quality Memory Foam is usually over 5 lbs/cu ft and high quality Polyfoam (HR grade) is 2.5lbs/cu ft or higher.

Durability

How long a material will keep its desirable properties and used also to indicate how long a material will take to completely break down.

Hysteresis

This is the amount of energy that is absorbed by a material and dispersed through the layer. it is the opposite of resilience. Memory foam for example has low resilience (it does not allow a ball to bounce) and high hysteresis.

IFD

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.

ILD
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.
Innerspring

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

A layer that used over an innerspring to both protect the layers above it an 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.

Intangibles

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.

Latex

A foam that is made from either natural latex from the rubber tree or from a chemical called SBR. It is usually made into a foam in one of two ways, either Talalay or Dunlop. In its natural or blended form is considered to be among the highest quality foams available and has very good point elasticity, support factor, and resilience.

Memory Foam

Also called visco-elastic or slow response foam, it is a special formulation of polyfoam which changes phase and becomes partly viscous instead of elastic with the application of heat and pressure. This allows it to form a very conforming pressure relieving cradle. It also has low resilience and when softened with heat, humidity, or time typically has a very low ILD (usually below 18).

Natural Fibers

Any fiber that comes from a natural rather than artificial source and is made through natural means. Wool, cotton, silk, horsehair are examples. They can be used a layer of a mattress or woven into a fabric.

Point Elasticity

The ability of a material to compress in a very small area without affecting the area beside it. Viscous materials are not elastic however they respond to the area of compression exactly so for the sake of simplicity (although not exactly accurate terminology) we refer to all materials of this type as point elastic. Higher point elasticity translates into a better ability to form a pressure relieving cradle that forms itself to the exact profile of your body.

PPP

A term used on the site that stands for Posture and alignment, Pressure relief, and Personal preferences. These are the 3 main criteria that defines "your perfect mattress" and the goal of all mattress design and theory is to match these basic needs and preferences to the unique body type, sleeping style, and individual preferences of each person.

Pressure Relief

The ability of a material to form a cradle to the shape of a body which redistributes weight over the surface of the mattress and relieves pressure on the body prominences or pressure points of each sleeping position. Different designs, materials, and mattress layering and construction methods have differing abilities to relieve pressure depending on each persons body type and sleeping style.

Resilience

This is the amount of energy that is stored by a material and causes it to "bounce back" after a weight is removed. It is also connected to how quickly the material bounces back. It is measured by dropping a ball on a material and measuring the height of the bounce as a percentage of the height from which it was dropped. Higher resilience polyfoam is often higher quality than lower resilience polyfoam and resilience is an important part of both the feel of a material and it's ability to allow freedom of movement.

Response Curve

This is the graph produced by the increasing amount of resistance to pressure of a material. Higher response curves allow a material to be both more pressure relieving with initial compression and supportive with deeper compression. Very similar to Comfort Factor. An upward curve is "better" than a straight line.

Sinking Down

This is used in a specific way on this website. It means how far in total the heavier parts of your body sink into a mattress in total. It determines spinal alignment rather than pressure relief.

Sinking In

This is used in a specific way on this website. It means how deeply you sink into a comfort layer material and the depth of the pressure relieving cradle that is formed. It is different from "sinking down".

Spinal Alignment

The goal of perfect support is to keep the spine in its natural alignment in all sleeping positions.

Support

A term often misused in the industry. It is a measure of how well a mattress supports and maintains the neutral alignment of the spine and joints. The primary support or deeper layers are mainly responsible for stopping the heavier pelvic girdle from sinking down too far into the mattress relative to the other lighter parts of the body while the upper or comfort layers provide the secondary or lighter support which fills in the gaps in the sleeping profile (like the waist or lower back) and helps to maintain the inward curves of the body and the spine in natural alignment.

Support Factor

This is the 65% IFD (how much weight it takes to compress a material 65% of it's thickness) divided by the 25% IFD. It is a measurement of the progressive resistance of a material. Higher quality materials will have a higher progressive resistance and although it is less well known or talked about in the industry, it is at least as important as ILD in determining the comfort and support qualities of a material.

Value

The price paid for a product in comparison to its benefits.

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