How many layers of fiberglass cloth will it take to build up 1/4 inch of solid glass?

There are several different types of fiberglass cloth available, such as woven, biaxial, etc. In the United States, fiberglass cloth is specified by its weight per square yard. For example, 6 oz. fiberglass cloth weighs 6 oz. per square yard. In addition, each fabric weight will have a different thickness. Some of the more common types of fiberglass cloth are shown in the table below.

To calculate the number of layers of fiberglass cloth needed to build a specific laminate thickness, divide the desired thickness by the thickness of a single layer of the type of fiberglass fabric you want to use.

The examples below indicate how much biaxial fiberglass cloth is needed to build a 1/4" thickness of glass. Note that biaxial cloth or biax is available with or without mat backing, and each type has a different weight.

Example 1: Biaxial Fabric without mat backing

• Fabric Weight = 17 oz. (per square yard)
• Single layer thickness = .035" (average of multiple layers applied using hand layup method)
• To build up 1/4" of biaxial fiberglass cloth, you would need approximately 8 layers.
  .035" x 8 = .28 (or approximately 1/4")

Example 2: Biaxial Fabric with mat backing

• Fabric Weight = 24 oz. (per square yard)
• Single layer thickness = .042" (average of multiple layers applied using hand layup method)
• To build up 1/4" of biaxial cloth with mat backing, you would need approximately 6 layers.
  .042" x 6 = .252 (or approximately 1/4")