| Silicone Sponge Silicone sponge, or closed cell | | | | subject to rain and harsh outdoor conditions. One |
| silicone sponge, is derived from a thin sheet of | | | | downside of closed cell silicone sponge products is |
| uncured silicone gum. The silicone gum compound | | | | the inability to achieve flame ratings beyond |
| is mixed with pigment and other ingredients during | | | | UL94HB. Silicone Foam Silicone foam is normally |
| a rigorous mixing process. The still uncured silicone | | | | considered to be an open cell, lightweight product |
| is then rolled into thin sheets and heat cured in a | | | | cast from low-viscosity, liquid silicone ingredients. |
| high temperature press or similar procedure. At | | | | These ingredients are catalyzed, rapidly mixed, |
| this point in the process, the silicone expands. The | | | | and cast onto a smooth, plastic liner. The cast |
| product is then often submitted to an additional | | | | foam is dispensed in a controlled thickness onto |
| four hour post-curing process at 480°F in a | | | | the plastic liner. It is then passed through a curing |
| hot-air, circulating oven to enhance the | | | | oven, and post-cured to drive out residual |
| compression set properties and reduce the | | | | moisture or vapors. The finished product typically |
| incidence of out-gassing in the final assembly. | | | | has a smoother surface. The lower density |
| Typically, the silicone is cured on a Teflon-coated, | | | | grades of cast silicone foams are typically not as |
| fiberglass bleeder cloth. Doing this allows gasses to | | | | successful in harsh-environment testing, such as |
| escape as the sponge expands during the curing | | | | wind-driven rains. Air and moisture can pass |
| process. Without the bleeder cloth, large air | | | | through low density open cell silicone foam unless |
| pockets would form that would affect the sealing | | | | the design allows for extensive deflection of the |
| properties of the gasket material. This is also | | | | gasket. Higher density silicone foams have been |
| what produces the fine, fabric surface finish on | | | | developed in recent years that permit good |
| the cured sponge, characteristic of all closed cell | | | | weather sealing with medium and firm density |
| silicone sponges. 'Closed cell' means that the cells | | | | silicone foam products. These higher density |
| are non-interconnecting, subsequently not allowing | | | | silicone foam products are actually composed of |
| water or air to leak through the sponge at low | | | | many closed cells. A major benefit of the liquid |
| pressures. Generally, the superior mechanical | | | | silicone foam product is the fact that it is |
| properties of closed cell silicone sponge provide | | | | flame-retardant, with many products meeting the |
| better weatherproofing than open cell silicones. It | | | | UL94V0 rating. |
| provides excellent sealing properties for products | | | | |