Open Cell Rubber
Open Cell Rubber
Open-cell sponge rubber is made from many of the same ingredients used in making solid rubber. One ingredient, however, that is added to all cellular rubber formulas and is not in a solid or dense rubber formula is a powder common blowing agent. In the case of open-cell sponge rubber sodium bicarbonate (baking soda) is normally used. When the uncured sponge rubber is heated in a mold, it expands or rises like a cake under low pressure and the baking soda introduces a network of open cells. By open-cell we mean that each cell is connected to the other with an opening so that water, air or gas can pass through them similar to the way water is absorbed by a dish sponge.
One outstanding characteristic of open-cell sponge rubber as compared to closed-cell sponge rubber is that open-cell has very good compression set. This is because the air rushes out of the open cells as the material is compressed. As soon as the pressure is released the air rushes back in and the material recovers to basically its full height. This material is recommended when the item will be repeatedly compressed yet must retain its original shape. It can be made into a variety of different rubber gaskets and rubber seals. Typical applications include shock absorption, cushioning, sound and vibration dampening, and gasketing.
In this context, the term foam denotes a specific manufacturing process where material is foamed into a cellular structure. The most well known foams are polyurethane foam, latex foam, and PVC.
Polyurethane foam is what is commonly used for the cushions on chairs and sofas. All foams are basically open-cell. The term foam denotes inherently a low-pressure process whereby the material is foamed onto a moving belt or into a contained area such as an open-top mold much the same way you would use a can of shaving cream. Once the material has jelled or set, you have a piece of foam. While there are some cells that are closed in any process, the predominant number of cells in a foamed product are open and none of these materials would pass the ASTM water absorption test. This test is a basic requirement of all truly closed-cell materials.
The chief characteristic of polyurethane foam as a gasketing material that makes it so attractive throughout the industry is its low price.