Backpack Construction

Backpack Foam

What is Open Cell Foam?

Open Cell Foam has interconnected air chambers throughout the material, which produces an extremely soft and highly compressible foam. Open Cell Foam is used in the construction of many high quality self-inflating camping mattresses. Whilst Open Cell Foam is very comfortable, self-inflating air mattress have a layer of air that provides support and insulation properties, and is highly compressible once the air is released. Open Cell Foam is not very good as a solitary padding material for backpacks. The high compressibility of the Open Cell Foam can cause shoulder straps and hip belts to over compress under load, providing minimum of comfort. While the padded straps may look great and feel wonderfully soft at the time of purchase, this will not be the case when the backpack is under full load. Determining whether the padded straps are Open Cell Foam is easy enough, simply squeeze with you hand, and if the straps compress to less than one half of the original size it is Open Cell Foam.

What is Closed Cell Foam?

Closed Cell Foam has open air chambers surrounded by foam that are not interconnected. The completely encapsulated air cells in the Closed Foam do not compress easily yet provides good padding. Closed Cell Foam is used in the production of Closed Cell Foam mats and its construction prevents full compressibility.. Since the Closed Cell Foam is a rubber based material and has completely encapsulated air chambers, it provides excellent insulation and absorbs very little water. For many years, better backpack designers cut and sewed the Closed Cell Foam into fabric sleeves providing the main source of shoulder and hip belt padding. The foam is dense, impervious to perspiration, and very comfortable. Closed Cell Foam is the main material used in backpack padding today, and it is a perfectly good material for backpack straps and hip belts. Determining whether the padded straps are Closed Cell Foam is easy enough, simply squeeze with your hand, and if the straps compress very little, then it is Closed Cell Foam.

What is Dual Density Foam?

Concluding that Open Cell foam is more comfortable next to the body (more compressible, therefore softer) and Closed Cell foam is better next to the load (less compressible, therefore firmer), several manufacturers use Dual Density Foam in padding their backpacks. Backpacks with Dual Density Foam capitalize on the advantages of both foams, placing the Open Cell Foam against the body and the Closed Cell Foam against the load. This combination is more comfortable than either Closed Cell Foam or Open Cell Foam, supporting the load well and providing comfort for body.

What is Compression Moulded Foam?

One manufacturing drawback to Closed Cell Foams concerns the manner of its fabrication. The material is typically poured into a frame and cooked into flat sheets that are cut to size, then cut to create a desired shape. The cost of cutting and shaping foam is highly labour intensive and results in significant material wastage. Because of these reasons another process was developed for the shaping, forming and customization of the next generation of foam, Compression Moulded Foam.

Compression Moulded Foam originally appeared in European backpacks in the late 1980's and used a different manufacturing technique. The outer nylon material is adhered to a block of polyethylene foam using a heat sensitive adhesive, and then the entire assembly is heated so that the foam and adhesive soften. At this point, the assembly is compressed into a shaped mould to provide the final product. The shaped hip belt, shoulder strap, or lumbar pad is then cooled to re-solidify the foam and adhesive. The final product is a pad shaped into a customized form.

Compression Moulded Foam is Closed Cell Foam, although slightly lighter in weight and shaped to the body without cut edges. An added benefit is the cavities formed inside the moulded foam pads, and different densities of foam can be included to provide flexibility to the final shape.