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Foam Utilization in Orthotic Therapy

Foam materials are a regular part of orthotic device composition and soft tissue supplementation. While firmer materials are used to contour to the plantar foot surface, providing less aggressive restraint to foot motions, flexible/compressible foams are routinely added as soft tissue supplementation on foot orthoses.

When soft or medium density foam materials are layered over an orthotic shell with contours specific to a patient's foot, it further reduces the potential for increased tissue compression at any one particular area. Greater padding effect is achieved by distributing compression load over more surface area against the foot. This is preferable to flat padding material or prefabricated shapes used in a shoe.

The types of foams available for application are limited and specific to desired comfort requirements that also match the need for control and level of activity of your patient.

There are two distinctly different types of foam, open-cell and closed-cell. Both types have application in orthotic therapy. Beyond these two primary types, material composition offers the next most distinguishing properties applicable in orthotic therapy.

Open Cell Foam:

Open-cell foam is soft cushioning material like that molded around a disabled person who is confined to a wheel chair or bed. Within the material, cell membranes, or surfaces of bubble like walls, are broken and air fills all of the spaces in the material. This makes the foam soft or weak, as if it were made of broken balloons or soft toy rubber balls.

By far, the most common open-cell foam used in orthotic fabrication is Poron ® . This urethane foam has been widely applied over several decades to reduce repetitive compression forces under foot. It is compression-set resistant, fungal resistant and breathable.

Biomechanical Services uses exclusively light blue, medium density shoe grade Poron ® for extensions and covers of open-celled foam. It can be applied to any orthotic model in our product line.

Closed Cell Foam:

Closed-cell foam can be soft or hard. It is dependent on how dense a material is used to surround the imbedded bubbles or cells, the size of the cell and how much compression is required to retain air or gas trapped within the cell membrane.

The cells or bubbles in the foam, not broken initially; resemble inflated balloons or soccer balls, piled together in a compact configuration. This makes the material strong or rigid because the bubbles are strong enough to take a lot of pressure, like the inflated tires that hold up an automobile.

Open-celled material is subject to break down, as cell walls break apart letting trapped air/gas escape under repeated load/compression. This leaves the material venerable to “taking a set”. Its cushioning advantage is lost as the area under greatest load mats down, molding around individual foot contours.

Biomechanical Services offers a substantial variety of closed-cell foams available for orthotic application and soft tissue supplementation, categorized below by material composition:

Polyolefin – is lightweight, easy to form, with excellent washable surfaces.
Polyfoam ®
Plastazote ®

Synthetic Rubber – was originally developed as an oil-resistant substitute for natural rubber. It is extremely versatile, with many years of proven performance.
Neolon ®

Urethane – is free of PVC, latex, and solvents, which offers lasting comfort, durability and biocompatibility.
Ultra Cloud ®

Silicone – is consistent in density with plantar fat pad of the foot and is made in both open and closed-cell structures.
Silipos ®

Foam Combination Layering

The best material combination under foot is achieved by layering soft closed-cell foam over open-cell foam. This provides softer padding against the foot that will form fit under compression, along with medium density foam that maintains shape and rebound affect against the shoe.

Research has shown that medium density materials are better for distributing compressive loads as they do not bottom out as consistently as softer materials and do not create irritation points as easily as harder materials.

Foam layering has the advantage of combining materials that forms to the foot, improving the spread of compressive loads, and further improving the medium density affect by using a more responsive material against the shoe.

Poron/Neolon is the best combination for athletes and active patients.

Poron/Polyfoam is a good combination for activities of daily living.

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