Although cushions may look similar in design on the outside, the materials used on the inside can have a significant impact on their performance. Understanding how materials perform will improve the clinician's ability to select a cushion based on their client's goals. This article describes materials, their benefits, and the clinical considerations when selecting the most appropriate wheelchair cushion.
Foam is a material which is formed by trapping pockets of gas. It can be a variety of densities, firmnesses, and weights. Based on the uniformity of the cells, they will be more or less rigid.
Closed cell foam has a uniform cell structure which creates rigidity. Open cell foam is softer due to a less uniform cell structure.
The weight of a foam is dependent upon mass, not upon firmness or density. Therefore rigid foam may also be lightweight, whereas softer foam may be heavier.
Memory foam (viscoelastic) has increased viscosity and density which allows it to slowly return to its shape after compression.
Elastomer is a man-made polymer with varying degrees of viscoelasticity.
In wheelchair cushions, an elastomer is often a matrix-like polymer structure.
Immersion is dependent upon the softness of the elastomer. It has a greater durability than foam over time.
Gel is a solid jelly-like material that can have properties ranging from soft and weak to hard and tough.
Although it is mostly liquid, it behaves like a solid. Therefore it has some viscosity, but does not allow for complete immersion.
Gel maintains its shape even when opened or cut.
JAY Flow Fluid is a non-Newtonian fluid. A non-Newtonian fluid remains in a semi-solid or highly viscous state.
In a non-Newtonian fluid, viscosity changes when under force to either more liquid or more solid.
Although a non-Newtonian fluid can take a shape without a container, it will flow with pressure. Therefore it needs to be contained when used in a cushion.
Air is a Newtonian fluid. A Newtonian fluid maintains its viscosity independent of stress. A Newtonian fluid only changes its viscosity in response to temperature.
If you provide a Newtonian fluid with stress, it will remain the same thickness (viscosity), but if you heat it up or cool it down it can become more liquid or more solid.
Newtonian fluids such as air or water cannot maintain a shape without a container. However, if the container is opened, it will spill and be released, thereby negating its efficacy.
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