Foam dielectric cables are noted for their low loss characteristics. Attenuation loss in a foam dielectric cable (a) normally is not quite as low as that in an air dielectric cable especially at higher frequencies (see MIL-C-22931 and MIL-L-3890), but (b) is approximately 15 percent lower than the attenuation in a solid polyethylene dielectric cable of a correspond ing size (see MIL-C-17). The average power rating of foam cable (as limited by temperature rise) is between solid polyethylene (which has a lower power rating) and air dielectric (which has a higher power rating) for corresponding cable sizes. Even though foam cables have a greater attenuation loss than corres ponding air dielectric cable, the foam cable has one major advantage in that it does not have to be pressurized with dry air or nitrogen.

Type I cable is unjacketed, and is therefore approximately 10 to 15 percent more economical than the jacketed version. Type I is not recommended for use in a corrosive atmosphere such as on shipboard.

Type II cable is identical to type I, except that it has a polyethylene jacket for corrosion resistance. Type II is recommended for shipboard application because of its resistance to a salt water atmosphere.