Whether you're admiring the sleek hull of a center console at the marina or performing your own fiberglass repairs in the driveway, you’re looking at one of the most important—and often underappreciated—elements in boat construction: resin. Resin is the binding agent that holds fiberglass cloth or mat together to form the hard, durable, and waterproof shell that defines modern fiberglass boats. But not all resins are created equal, and understanding the types, sourcing, applications, and techniques—both for pros and DIYers—can make a big difference in boat building and repair outcomes.


Fiberglass and resin

Above: A worker in a protective mask uses resin and fiberglass to construct a boat hull. Image via Pond5.


What Is Resin?


Resin is a liquid thermosetting polymer that hardens when mixed with a catalyst or curing agent, typically creating a rigid, solid matrix. In fiberglass boat construction, resin is used in conjunction with reinforcing materials like fiberglass cloth, mat, or woven roving to create a composite structure that is lightweight, strong, and corrosion-resistant. Once cured, the resin-fiberglass matrix forms the basis of the hull and deck of most recreational boats built today.

Types of Resin Used in Fiberglass Boat Building


Several different resins are used in fiberglass boat building, each with its own properties, price point, and ideal application. The three most common types are:

1. Polyester Resin


This is the most widely used resin in fiberglass boat construction due to its affordability and ease of use. Polyester resin cures relatively quickly and bonds well with fiberglass. However, it has a higher shrink rate during curing and less resistance to water absorption over time compared to other resins.

2. Vinylester Resin


Vinylester resin offers improved water resistance, strength, and flexibility compared to polyester. It’s more expensive but is often used in high-performance hulls, racing boats, or applications where blister resistance and durability are critical. It also provides better bonding properties and lower shrinkage.

3. Epoxy Resin


Epoxy resin is the gold standard for high-strength, low-shrink, and moisture-resistant applications. It provides superior adhesion, especially when used in repairs or on wood substrates. Epoxy is more expensive and has a more demanding mixing and curing process, but it's a favorite among custom builders and advanced DIYers.

How Resin Is Used in Boat Construction


Resin is applied to fiberglass reinforcement in a variety of methods, depending on the build technique and the type of vessel being produced. Here's a breakdown of the most common processes:

Hand Lay-Up


One of the oldest and simplest methods, hand lay-up involves laying sheets of fiberglass fabric into a mold and manually saturating them with resin using rollers and brushes. It’s labor-intensive but cost-effective and offers precise control over thickness and shape.

Spray-Up


In this method, chopped fiberglass strands and resin are sprayed into a mold using a chopper gun. It’s faster than hand lay-up and suitable for large hulls and components, but can lead to inconsistent laminate thickness if not carefully controlled.

Vacuum Infusion


This more advanced method uses a vacuum pump to draw resin into dry fiberglass laid in a mold and covered with a plastic film. It produces high-strength, consistent laminates with reduced resin use and emissions. Many high-end production boat builders use vacuum infusion or resin transfer molding (RTM).

Where Resin Comes From: Sourcing and Manufacturing


Most boat-building resins are derived from petrochemicals. The base material, often styrene, comes from crude oil. Manufacturers blend it with other chemicals like methacrylic acid or bisphenol-A to form the various resin types. These are typically produced by major chemical manufacturers such as Ashland, Reichhold, or Interplastic Corporation and then sold to marine supply companies or directly to boat builders in bulk.

As sustainability becomes more of a focus in the marine industry, some companies are exploring bio-based alternatives derived from plant oils or recycled materials. While not yet widespread, they represent a promising development in reducing environmental impact.

The Impact of 2025 Tariffs on Resin Costs and Availability


The 2025 U.S. tariff policy announced by Donald Trump and his administration has significantly impacted the resin market, particularly for boat builders and DIY enthusiasts. In April, the administration imposed a 10% universal tariff on all imports, with higher rates for specific countries. Notably, Chinese goods, including many resin products, faced tariffs up to 145%, later reduced to 30% during a 90-day truce period. Despite this reduction, the remaining tariffs continue to exert pressure on resin costs and availability.

These tariffs have disrupted supply chains, leading to increased resin prices and uncertainty in the market. Many U.S. businesses that rely on imported resins from China and other affected countries have experienced delays and higher costs, prompting some to seek alternative suppliers or consider domestic options. However, the sudden shift in sourcing has not been seamless, as domestic production may not immediately meet the increased demand, potentially leading to shortages and further price hikes.

For boat builders and DIYers, this means planning projects with greater foresight, considering potential delays in resin availability, and budgeting for higher material costs. Staying informed about the evolving trade policies and maintaining flexibility in sourcing strategies will be crucial in navigating the challenges posed by the 2025 tariffs.

How the Pros Use Resin in the Shipyard


Professional boat builders carefully select resins based on the part of the vessel being produced. For example:

  • Hulls: Often built with vinylester or polyester resin for strength and water resistance.

  • Decks: May use polyester for affordability or vinylester for added durability.

  • Structural reinforcements: May involve epoxy for bonding critical components or during secondary bonding operations.


Temperature and humidity control are crucial during curing, as improper conditions can lead to incomplete curing, delamination, or voids in the laminate. Boatbuilders also use gelcoat, a pigmented form of resin, as the outermost layer for color and UV protection. After the gelcoat is sprayed into the mold and partially cured, the fiberglass layup begins on top of it.

The professional process also includes meticulous timing for layup, rolling out air bubbles, and monitoring cure progression. Many yards operate under ISO 9001 or ABYC standards to ensure consistency, safety, and quality assurance in composite manufacturing.

DIY Boat Repair: Working With Resin at Home


For boat owners interested in tackling their own fiberglass repairs, resin can be your best friend—or your biggest frustration—depending on how you handle it. Here are some tips for getting it right:

Choosing the Right Resin



  • Polyester resin is ideal for non-structural repairs and compatible with original construction on many production boats.

  • Epoxy resin is best for bonding, wood repairs, or where strength and water resistance are key. It also adheres well to cured polyester laminates, while polyester does not bond well to cured epoxy.


Safety First


Always wear gloves, eye protection, and a respirator. Work in a well-ventilated area, especially when using polyester or vinylester, which emit strong fumes due to their styrene content.

Mixing and Application


Use precise ratios when mixing resin and hardener or catalyst—usually provided by the manufacturer. Too much hardener can lead to overheating and cracking; too little may prevent full curing.

Apply the resin with disposable brushes or rollers and use fiberglass cloth or mat to reinforce the repair. Use a plastic spreader or fiberglass roller to remove air bubbles and ensure a solid bond.

Sanding and Finishing


Once cured (typically within 24 hours), sand the area smooth and apply more resin or gelcoat for a finished surface. Use a UV-protective topcoat or paint to seal epoxy repairs, which can degrade under sunlight.

Common Pitfalls



  • Mixing errors – Inaccurate ratios can ruin a batch.

  • Contamination – Ensure surfaces are clean, dry, and free of wax, oil, or paint.

  • Working time – Each resin system has a “pot life,” the time before it begins to gel. Don’t overmix more than you can use in 10–15 minutes, especially in hot weather.


Final Thoughts


Resin may not be the flashiest material in the boatbuilding process, but it's the glue—literally and figuratively—that holds it all together. Whether you're a professional builder crafting performance hulls or a weekend warrior patching a cracked keel, understanding how resin works and choosing the right type for your application is critical for long-lasting results. As resin technology evolves and more sustainable options emerge, this essential material will continue shaping the future of recreational boating from the inside out.

Thinking about trying a fiberglass repair or building your own skiff? Start small, take your time, and respect the resin. It's a powerful tool—just be sure to mix it right, ventilate your workspace, and always read the label.

Written by: Ryan McVinney
C. Ryan McVinney is a film director, producer, writer, actor, boat captain, outdoorsman and naturalist. He's the host and director of the award-winning TV show Stomping Grounds that explores boating culture across America, sponsored by Boat Trader. McVinney also directs and produces the documentary series Cult Classics featuring top yacht builders and the extreme superyacht show LEGENDS for YachtWorld, as well the popular Factory Fridays video series for boats.com that visits boat building facilities around the world. He's a regular contributor to leading marine industry publications and regularly tests and reviews boats on his varied outdoor adventures.