Allied Encyclopedia – 3 Types of Insulation

We all know that cables are available in countless variations. From the materials used to the cable’s configuration, there are an infinite number of possibilities. A cable’s insulation alone is available in many different materials, and to make it even more complex, those materials can be processed using different methods to provide different physical and electrical characteristics. In this Allied Encyclopedia, we discuss the three main types of insulation produced by these methods: solid, semi-solid, and foamed.

Insulation is commonly available in three different forms:

    1. Solid
    2. Semi-Solid
    3. Foam

Solid Insulation – RG214 Coax

Solid insulation is the most common. It is also the easiest to apply and the least costly to produce. Because it is a solid layer of polymer, it does not require the more complex manufacturing processes involved in producing semi-solid or foam insulation.

Solid insulation is the densest of the three types, and although this gives it more mechanical strength, durability, flexibility, and crush and abrasion resistance, it usually increases the cable’s dielectric constant. This means that it does not have the electrical properties required for high performance cables, but it is sufficient for many other applications. It is used in just about every type of wire available, from everyday hook up wire to specialty coaxial cables such as RG 142 cable, RG 214 cable, and RG 400 cable.

Unlike solid insulation, foam insulation is cellular and composed of around 50% gas. The bubbles in the material are commonly air or nitrogen. These gases give the material a lower dielectric constant, meaning better electrical properties overall. This level of electrical performance makes foam insulation a common choice for high performance communication cables and coaxial cables such as LDF heliax coaxial cable, FSJ heliax coax, RG 307 cable, and more.

As an added benefit of the material’s strong electrical characteristics, a thinner wall thickness may be used to provide the same level of performance as a solid insulation with a thick wall. This can be a great benefit for applications with tight space requirements.

The downside of foam insulation is its complex construction. It is more difficult to produce than solid insulation, and great care must be taken to ensure that the gas bubbles in the insulation have consistent size, shape, and dispersion throughout the material. If these characteristics are not consistent, the performance of the cable is compromised. The added difficulty of manufacturing foam insulation is reflected in the price of the material, which is significantly more expensive than solid insulation.

Foam insulation does not have the mechanical strength of solid insulation either. Because it is less dense, it is less durable, less crush-resistant, and more likely to kink.

Semi-Solid Insulation – RG62 Coax

The third type, semi-solid insulation is defined by the air gaps in its material. In fact, it consists of more air than polymer. As a result, it has the lowest dielectric constant of the three types. It also has the least mechanical strength and durability. Semi-solid insulation can be found in different types of cables, including some M17 cables such as M17/30-RG62 Cable and M17/90-RG71.

The three different forms of insulation have distinct mechanical and electrical characteristics, making some types more appropriate to certain applications than others. Understanding these variations between solid, foam, and semi-solid insulation is the key to choosing the most appropriate type for your cable and application.

About awcwire
Allied Wire & Cable is a value-added manufacturer and distributor of electrical wire and cable, tubing, and more. We are a family owned and operated company, serving a wide range of industries, including the military, automotive, aerospace, and telecommunications markets. Allied is headquartered in Collegeville, PA. Additional locations can be found across the US, in Phoenix, AZ; Bedford, NH; Pewaukee, WI; Rochester, NY, Tampa, FL; and Mt. Juliet, TN. For more information on Allied, visit our main website at

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