When it comes to fiberglass there are so many options that it can be confusing. Don’t worry we are here to break it all down for you and make it easy to understand. First things first when looking at fiberglass you will see 2-3 main points about it.
First the weight, this is a measurement of the glass strands in ounces per a square yard. That means for a 6oz cloth if you were to cut out a square yard (3ft by 3ft) it would weight about 6 ounces. The second main point would be the width of the stated material. Typically cloth is sold by the linear yard, so when you see something like 6oz x 50″ you would be purchasing 1 yard long by 50 inches wide. The final main point is the style number. While this is sometimes listed when purchasing a cloth it is not always required as there are common styles within a typical weight. Most of the time the style will tell you what type of weave pattern there is to the material. Some weaves are for cosmetics, while others provide a higher strength.
There are 2 main types of fiberglass, woven and stitched. Each have their own advantages and disadvantages.
Woven Fiberglass
Woven fiberglass means that the strands of glass filaments are woven together much like a t-shirt . There are several styles to be woven with a few very common ones. The most common is a plain weave. What this means is each thread is woven over and under each other with no skipping threads or gaps in the pattern from strand to strand. The next common weave pattern is called 2x2twill or crows-foot weave. This is usually for a cosmetic appearance. This means that each thread goes over 2 threads then under 2 threads. You can typically see this in carbon fiber car parts. The final common weave is a tight weave. While there are 2 versions of the common tight weave, 4 harness satin or 8 harness satin, they give you higher physical properties compared to other weaves of a similar weight. Depending on which harness satin you are look at they will follow a pattern in their weaving. A 4 harness satin has each thread woven over 3 threads then under 1 thread, while an 8 harness satin goes over 7 threads and under 1 thread.
Stitched Fiberglass
Stitched fiberglass unlike woven fiberglass never has its glass filaments woven between the 2 main axes, meaning that there are 2 or more layers of glass filaments laying flat on top of each other. While there are several variations of these too they do have some very common characteristics. The main would be the number of layers. The most common would be a bi-axial or 2 layers. These 2 layers of glass are oriented in specific orientations to achieve different strength properties. The most common bi-axial would be in a +45 degree and -45 degree arrangement, forming what looks like an X when looking at the material. The 0 degree axis is known as the warp which runs from the first yard of the roll until the last yard. The 90 degree axis is known as the fill, which runs from side to side of the roll. There are also tri-axial and quadri-axial meaning they use 3 or 4 layers of glass filament.
Stitched fiberglass can also come in a varient with a layer of chopped strand mat on the back. While this is typically meant for people doing a polyester layup it is okay to use it with epoxy.
Chopped Strand Mat
While this is a less common fiberglass when it comes to epoxy it is worth mentioning. Chopped strand mat, or mat for short, has a few deviations from the common fiberglass. First thing that is different is that it is neither a woven or a stitched material. This material is strands of glass filament held together by what is called a binder or glue. Typically this is used in a polyester lamination.