Cushion Properties

Firmness does not describe density or durability, it describes the spring (ability to compress and rebound) of a foam.

The softness/firmness of the foam will impact positioning and pressure.

The clinician must select foams that are durable, yet provide the level of stiffness or softness to achieve the positioning goals.

The clinician must also consider the foam's reaction to heat (including body heat) because foam (i.e. memory foam) may soften when sitting on it, thus reducing the IFD.

Density is important to consider when selecting a cushion so it lasts the intended amount of years. Regardless of foam's IFD, it is important that high density foam is used. This is important because density, not firmness, influences durability.

Manufacturers who use low density foams may reduce cost, but ultimately sacrifice durability.

Cushions that use low density foams may compress over time (bottom out). They harden, lose shape, and no longer provide appropriate support and pressure distribution.

It is important to have a cushion which reduces reaction force as much as possible.

When a pelvis is seated, the ischial tuberosities are positioned at the maximum point of compression, resulting in high reaction force that often contributes to tissue breakdown and the formation of pressure injuries.

Hydrostatic loading evenly distributes pressure to reduce buildup under sensitive areas of the pelvis, which helps prevent the formation of pressure injuries.

Hydrostatic forces that are in balance give the feeling of weightlessness or floating in a pool.

It's important to provide the correct amount of fluid to enable proper reduction of hydrostatic forces.

Tension can cause increased forces at the point of greatest immersion, usually the area around the ischial tuberosities.

Foam is a prime example of a tension-producing cushion material, whereas fluids are tension-reducing.

Using materials such as 4-way stretch in covers reduces tension on the tissues. Although tension is a common concern in cover materials, it can also be a problem with the actual cushion material.

Sinking the pelvis into a cushion fluid (JAY fluid or air) or a pre-molded shape significantly increases contact area and helps reduce peak pressure areas.

The microclimate of an area while sitting on a cushion must be monitored to prevent temperature build-up which leads to moisture, maceration, and pressure ulcer.

Clinicians should consider microclimatic materials which cool the area and delay temperature build-up. Microclimatic materials will also reduce perspiration (moisture).

Although tissue breakdown has been attributed to excess heat and moisture, skin that is too dry is also more prone to pressure ulcer.

Microclimatic material encourages the passage of air, heat, and water vapor from the user; therefore materials that promote a stable microclimate in the cushion should be considered.

Cushions which provide vibration dampening to reduce the WBV are important for those who experience pain, fatigue, and nerve damage.

A vibration-reducing material should be able to perform over a wide range of temperatures while still absorbing shock and vibration energy.

Visco foam is an example of a material that performs well in absorbing shock and vibration.