Fiberglass is the superhero of DIY repair and construction projects. Whether you’re patching up your trusty boat, reinforcing a car panel, or working on a custom piece for your home, fiberglass has the strength, light weight, and versatility to do it all. But with so many types to choose from—cloth, mat, biaxial, woven roving, and more—it can be hard to know where to start.

What Is Fiberglass?

Fiberglass is a composite material made from ultra-thin glass fibers that are woven, stitched or bonded together to create a fabric or mat. It’s used in combination with a resin—typically polyester, vinyl ester, or epoxy—to create a tough, durable material.

This material excels in applications needing strength without excessive weight, which is why you’ll see it used in boats, car parts, surfboards, and even custom furniture.

Fiberglass is especially popular with DIY enthusiasts for its affordability, flexibility, and endless potential for creative and functional projects. However, not all fiberglass is the same, and choosing the right type can make or break the success of your project.

Now, let’s explore the key types of fiberglass materials and their best applications.

What Is Fiberglass Cloth?

Fiberglass cloth is made by weaving very fine glass fibers into a fabric. Its smooth texture and tight weave make it ideal for laminating projects where a polished surface is critical.

Key Features of Fiberglass Cloth:

• Thin and lightweight

• Provides a smooth, professional finish

• Best for small to medium scale precision projects

Best Uses:

• Surfboard construction and repairs

• Covering boat hulls or decks for a smooth look

• Patching up small, detailed areas like ding cracks

Fiberglass cloth excels in scenarios where aesthetics matter. The heavier it is, the more strength it adds.

What Is Chopped Strand Mat?

Chopped strand mat, commonly referred to as CSM, is a more rugged and malleable type of fiberglass. It’s made of randomly distributed short fibers bound together with a resin-soluble binder. When mixed with polyester or vinyl ester resin, CSM conforms to odd or complex shapes, making it perfect for repairs.

Key Features of Chopped Strand Mat:

• Non-woven, random fiber composition

• Easy to fit into irregular surfaces

• Provides thickness and prevents print- through

Best Uses:

• Boat hull patching including where contours are involved

• Automotive repairs, especially for irregularly shaped areas

• Reinforcement of structures needing extra thickness

• fiberglass molds

Do note that CSM is typically paired with polyester or vinyl ester resin. Epoxy resin does not dissolve the binders in CSM effectively which makes the two incompatible. So, make sure you’re using polyester or vinyl ester resins.

What Is 1708 Knit Biaxial Fabric?

One of the premier options for heavy-duty fiberglass applications, 1708 knit biaxial fabric combines a biaxial stitch pattern with a layer of chopped strand mat. This hybrid material offers strength in two perpendicular directions while retaining flexibility.

Key Features of 1708 Fabric:

• Stitched fiber layers for added strength

• Includes pre-attached CSM for convenience

• Makes for a stronger, more rigid laminate

Best Uses:

• Structural boat repairs or hull reinforcements

• Strengthening high-stress parts of a vehicle

• Large-scale industrial or commercial applications requiring rigidity

1708 fabric is a favorite among professionals and DIY enthusiasts alike for its ease of use and versatility. Since the chopped strand mat is stitched instead of using a binder, it is compatible not only with polyester and vinyl ester resin but with epoxy resin as well.

What Is Woven Roving?

Woven roving is another staple in fiberglass projects. Think of it as the “workhorse” of fiberglass fabrics, known for its outstanding strength and durability. It resembles a coarse, crisscrossed weave made of large fiberglass strands.

Key Features of Woven Roving:

• Thicker and heavier than cloth or mat

• Best for adding bulk and durability

• Highly resistant to impact stress

Best Uses:

• Laminating layers for boat deck construction

• Large flat areas

• Building frameworks or molds requiring extra resilience

While it lacks the smoother finish of fiberglass cloth, woven roving’s robustness makes it the go-to choice for flat, high-strength applications. It is recommended to layer with chopped strand mat. The mat will fill in the large holes in the woven roving and allow for better bonding.

How to Use Fiberglass Materials

Carefully working with fiberglass requires proper tools, preparation, and techniques. Here’s how to get started with the process, step by step.

1. Gather Your Materials

Before beginning, gather all the necessary tools and materials:

• Your chosen fiberglass material

• The right resin (polyester, epoxy, or vinyl ester)

• Hardener or catalyst for curing the resin

• Application tools (brushes, rollers, gloves)

• Sandpaper, scissors, and a finishing tool

• Safety equipment including gloves, respirator, eye protection

2. Cut and Arrange Your Fiberglass 

Pre-cut the fiberglass mat or fabric to the desired dimensions. If you’re layering different pieces, plan to overlap them slightly for extra strength.

3. Prepare Your Surface 

Proper preparation is critical to ensuring the fiberglass adheres correctly. Clean the surface thoroughly, removing dirt, grease, or old layers if you’re repairing something existing. Lightly sand the area to create an ideal bonding surface.

4. Mix and Apply the Resin

Follow the manufacturer’s guide to mix resin and hardener (or catalyst). Once mixed, use a brush or roller to apply a thin layer to the surface. Place your fiberglass fabric or mat on top of the resin.

5. Wet Out the Fiberglass

After positioning the fiberglass on your surface, “wet out” the material by applying more resin on top. Use your roller to work out any bubbles or wrinkles and ensure the fiberglass is fully saturated.

6. Layer as Needed

For added strength, apply multiple layers of fiberglass and resin. Let each layer cure before adding more fiberglass and resin. If using a polyester or vinyl ester laminating resin, there is no need to sand between coats (unless you have waited more than 2-3 days). If using a waxed resin or epoxy resin, you will need to sand between layers.

7. Allow to Cure and Finish

Once you’re done layering, allow the resin to cure according to the manufacturer’s instructions. Once cured, sand down any rough sections and apply a finish, such as gel coat or paint, for protection and aesthetics.

Master Fiberglass Projects with Confidence

If you’re ready to get started, assemble your materials, prep your workspace, and get building. Patience, precision, and a little practice make all the difference!