Comparing Stainless Steel, Polycarbonate and Fiberglass Reinforced Polyester Enclosures

  • September 01, 2015
  • Feature

Even seasoned enclosure specifiers can find it challenging to choose the optimum material for achieving long-term product service life while meeting all application requirements. Depending on the application, stainless steel and non-metallic enclosure materials, such as polycarbonate and Fiberglass Reinforced Polyester (FRP), can offer solid performance benefits.

Material Overview – Metals

Corrosion resistance is an important property for all enclosure materials, including metallic enclosures. Some metals, such as gold, platinum and palladium, do not corrode at all, though they are not ideal for enclosure purposes due to their high cost. Almost all other metals corrode, and the rate at which corrosion happens depends on the type of metal and the environmental conditions it endures. 

Stainless steel is a commonly chosen enclosure material due to its reputation for high corrosion resistance. The special property that makes stainless steel naturally resist corrosion is that it contains approximately 10.5% chromium. When chromium comes in contact with oxygen, it forms a film on the surface of the material, creating a natural protective barrier that is resistant against corrosion. This unique property allows stainless steel to withstand harsh environments for years with reliable protection against corrosion. Specifiers should be aware, however, that there are some factors that can compromise the natural protective film on the stainless steel.

Another reason that specifiers commonly choose metal enclosures is based on their reputation for strength. Strength measures the resistance of a material to failure, while material toughness measures its ability to withstand sudden impact. Increasing toughness usually decreases strength, and vice versa. What specifiers may not know is that even though stainless steels have high strength, they exhibit low toughness, allowing them to dent easily. When a stainless steel enclosure becomes dented, the integrity of the box is compromised because it will not have a flush seal. An enclosure that is not flush creates a situation where the seal loses its capability to be air and water tight. In addition, there exists the possibility for compromised security, as the controls may become easy to access. 

Polycarbonate Enclosures: The Basics 

Polycarbonates are a group of thermoplastic polymers. They are easily worked, molded, and thermoformed. Due to this versatility, polycarbonates are very widely used for enclosure applications.

Key features of polycarbonates include:

  • Good UV performance
  • Flexible and tough
  • Good temperature range (-20 degrees F to 240 degrees F)
  • Fair chemical resistance
  • Fair ease-of-processing
  • Easy to modify
  • Fair water absorption
  • Self-extinguishing flammability

There is occasional confusion surrounding the use of polycarbonates for enclosure applications because there are a wide variety of polycarbonate options available. Additionally, materials suppliers often offer variations within the group classification. For example, some polycarbonate enclosures might feature UV stabilizers, added to help protect the material from the effects of sun exposure, whereas others may have minimal or no additive UV protection. Therefore, it is essential to determine the necessary performance level based on the demands of the environment in which the enclosure will be used. For example, for an enclosure to perform optimally in exterior applications, the material will potentially require enhanced UV protection to prevent degradation.

Another variable to consider is that some polycarbonate formulations include glass fibers. Although this characteristic can significantly increase tensile strength, flexural strength, flexural modulus, and heat deflection temperature of the polycarbonate, it can also cause a decrease in impact strength and tensile elongation. Each of these properties increases with the amount of glass fiber added to the polycarbonate. Again, proper specification should be made according to the ability of the material to withstand specific environmental demands during its product life span, on-the-job. An understanding of environmental conditions that will impact the enclosure will determine the level of corrosion risk and the best material choices for preventing the high cost of corrosion damage.

Fiberglass Composites: The Basics

Thermoset materials, such as polyester resin, are combined with glass to create a unique composite called Fiberglass Reinforced Polyester (FRP). FRP performs exceptionally well, exhibiting high durability and weather ability. FRP also provides the highest degree of corrosion resistance in most environments.  

Key features of FRP include:

  • Excellent UV performance
  • High rigidity
  • Very good temperature range (-31 degrees F to 266 degrees F)
  • Excellent chemical resistance
  • Good ease-of-processing
  • Easy to modify
  • Good water absorption
  • Self-extinguishing flammability

Although metal enclosures are sometimes thought to possess benefits in terms of strength, an even greater advantage of FRP materials is the ability to withstand significant impact without permanent deformation or denting. Fiberglass also offers an effective continuous service temperature range, allowing enclosures molded from FRP material to withstand even the harshest industrial operating environments.

FRP composites also compare favorably to metallic enclosure options in that they are easy to modify using commonly available tools. Additionally, many FRP composite enclosure manufacturers offer in-house options for factory-based modifications.

FRP enclosures are durable, corrosion resistant, and easily adaptable for many demanding applications. Perhaps the all-encompassing advantage of choosing an FRP composite is the reliable performance and duration of service life of the unique material properties. 

One of the primary differences between brands of FRP materials relates to the ability to endure long-term exposure to UV rays. Stahlin Non-Metallic Enclosures feature SolarGuard, a non-halogenated fiberglass formula system that beats the effects of outdoor exposure, as well as provides chemical and flame resistance. SolarGuard, in extensive comparison testing, outperformed other available SMC formulations by as much as 60% in its ability to retain gloss and color after exposure to concentrated UV light.


All enclosure materials ---- stainless steel, polycarbonate and FRP --- will provide protection in a variety of applications. It is critical to evaluate the environmental factors of the application where the enclosure will be used. By using such information in tandem with the materials knowledge presented here, engineers can specify the best material for the project, thereby guaranteeing long-term reliability and reduced overall costs. Performance of the material matters! 

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