When I finish a woodworking project, I want it to feel finished—not just well-built, but protected and complete.
A good finish adds that final touch.
It brings out the grain, protects the wood, and helps the piece last.
And if you’ve ever stood in the aisle trying to choose between polyurethane and varnish, you know it’s not always an easy call.
I’ve used both over the years, and each has its place.
In this post, I’ll break down what makes them different, when to use each one, and which finish might be the better choice for your next project.
What Is Polyurethane?
Polyurethane’s been around for nearly a century. It was originally used in everything from foam insulation to shoe soles, but today it’s one of the most common finishes in the woodworking shop.
I like it because it’s durable, non-toxic when cured, and food-safe—so I don’t think twice about using it on cutting boards or furniture.
When applied right, it creates a hard protective surface that really holds up over time. It’s also taken over as the go-to finish for most projects, replacing varnish in a lot of cases.
So, what exactly is it made of?
Polymers
This gets a little technical, but stick with me. Polymers are just large molecules—basically chains of smaller units linked together. Some are synthetic, like nylon and epoxy. Others are natural, like wool or even DNA.
We’re not coating our projects with Teflon or silk, obviously—but polyurethane does act like a tough plastic shield. It locks out moisture, resists heat, and helps your piece survive real-world use.
Urethanes
Urethanes are in the rubber family, and when you combine them with polymers, you get polyurethane. The two parts react through a process called polymerization—that’s the chemical magic that gives polyurethane its strength and durability.
So, in plain terms: polyurethane is a plastic-like topcoat that cures into a hard shell to protect your wood. Simple as that.
A Quick History of Polyurethane
Polyurethane was first developed in the 1930s by a chemist named Otto Bayer. During World War II, it was even used as a protective coating on airplanes.
Over time, it found its way into everything from furniture foam to clothing—and eventually into our woodworking shops.
Today, it’s one of the most popular finishes around because of how tough and reliable it is.
Types of Polyurethane
Polyurethane is basically a mix of polymers and urethane, but it needs something to carry it. That’s where the two main types come in: water-based and oil-based.
Each one has its strengths depending on your project and how much time (or patience) you’ve got.
Water-Based Polyurethane
Water-based poly is probably the most common for DIY projects. It dries fast, has low odor, and doesn’t yellow over time. You’ll need multiple coats for solid protection, but newer formulas have made that easier.
I reach for water-based poly when I want a clear finish and a quicker turnaround.
Oil-Based Polyurethane
Oil-based poly is the heavyweight. It’s thicker, takes longer to dry, and has that warm amber tone a lot of people love.
But it also comes with strong fumes, a longer cure time, and more safety precautions.
I always use a respirator with this stuff—and even then, it’s best saved for big projects where durability really matters.
Applying Polyurethane to Your Project
Polyurethane can be applied in a few different ways, and each one has its pros and cons.
Here’s how I usually think about it when planning a finish.
What You’ll Need
Depending on how you want to apply the poly, here are your main options:
- Brush (Synthetic or Natural Bristle):
Good for full coverage but can leave brush marks or bubbles. Foam brushes help reduce that. - Rag (Wipe-On Poly):
Great for thin, even coats without bubbles. Ideal for smaller projects or when you want more control. - Sprayer (My Go-To):
Offers the smoothest, most consistent finish with no brush marks. Requires thinning the poly and good ventilation.
How to Apply It
- Prep the Surface
Sand the wood smooth and remove all dust. Poly will highlight any flaws you leave behind. - Choose Your Application Method
- Brush it on if you’re working on large flat surfaces and don’t mind a little extra sanding between coats.
- Wipe it on for a cleaner, thinner application—especially useful for touch-ups or detailed pieces.
- Spray it if you want the most even finish and have a good spray setup. Thin the poly as needed.
- Apply Multiple Thin Coats
I usually do 3–5 coats, letting each one dry fully and sanding lightly between them with a fine-grit pad or paper. More coats = better protection. - Avoid One-Coat Products (For Now)
There are polys that claim to do the job in one coat, but they’re thick, hard to apply, and honestly more hassle than they’re worth. I haven’t found a reason to switch yet.
For me, water-based poly is the default unless I have a reason to use something else.
It’s fast, easy to work with, and holds up just fine for most indoor projects.
What Is Varnish?
Varnish is another clear finish that’s been around forever in the woodworking world.
It forms a hard, protective layer over the wood and brings out the grain in a way that still feels natural. It’s usually made from a mix of drying oils, resins, and solvents, and it cures either through evaporation or by reacting with oxygen in the air.
What makes varnish different from polyurethane is how it cures and what it’s made from—but in the end, they both do the same job: protect the wood.
Varnish resists moisture, scratches, and fading. You’ll find it in gloss, satin, and semi-gloss options, and it can be brushed, rolled, or sprayed on.
It’s not a tricky finish to work with, but like anything, it takes some patience. Thin coats, full dry time between each, and light sanding go a long way toward a great result.
Marine and Spar Varnishes
There are a couple of specialty varnishes worth knowing about if you’re working on outdoor projects.
- Marine Varnish: Built for boats, this stuff is loaded with UV blockers and holds up to sun, water, and salt. It’s one of the best choices for harsh outdoor conditions, but it’ll need to be reapplied every few years to stay effective.
- Spar Varnish: Originally used on the spars of sailing ships, spar varnish is flexible and built to handle movement, moisture, and sun. It’s a solid option for anything that lives outdoors—like Adirondack chairs, planters, or garden benches.
Both marine and spar varnish are available in oil- and water-based forms and in various sheens.
They’re easy enough to apply and provide long-lasting protection if you follow the basic steps: thin coats, full drying time, and reapplication every few years if the piece lives outside.
Polyurethane vs. Varnish: Which One Should You Use?
Now that we’ve looked at both finishes, let’s break down where each one shines—and where it might fall short.
Both polyurethane and varnish are clear finishes that protect wood and bring out its natural beauty.
They’re available in oil-based and water-based forms, and both can hold up well when applied properly. But they behave a little differently, and that can make all the difference depending on your project.
Key Differences
- Varnish is the more traditional finish. It’s made from natural resins and solvents like turpentine, and it forms a flexible, protective film. It’s great at resisting moisture and sun damage—especially in outdoor environments.
- Polyurethane is a newer, synthetic finish. It cures into a harder, more durable surface that holds up better against water, chemicals, and heavy wear. It’s especially popular for high-traffic furniture, flooring, and cutting boards.
Which One’s Better?
It depends on what you’re working on. Here’s how I decide:
- Type of wood: I lean toward varnish for softwoods, since it’s a little more forgiving. For hardwoods, polyurethane gives better surface protection.
- Indoor vs. outdoor: Polyurethane works great indoors, but if the piece is going outside or will see sun exposure, varnish (especially spar or marine) is the better choice for UV resistance.
- Your preferences: If you like a more natural look with less sheen, varnish might be your finish. If you want tough-as-nails durability, poly is hard to beat—even if it can look a little plastic.
Pros and Cons at a Glance
Varnish
Pros:
- Easier to apply
- More natural-looking finish
- Better UV protection
- Less toxic during application
- Budget-friendly
Cons:
- Not as tough as polyurethane
- Less resistant to chemicals and water
- Can yellow over time
Polyurethane
Pros:
- Extremely durable
- Excellent water and chemical resistance
- Doesn’t yellow with age
Cons:
- Can be harder to apply smoothly
- Strong fumes (especially oil-based)
- Slightly plastic-looking finish
- Not great for sun exposure
At the end of the day, both finishes have earned their place in the shop. I keep both on hand and choose based on the project.
Whether I’m finishing a cutting board or sealing up some outdoor furniture, there’s always a right tool for the job—and that includes the finish.
Polyurethane vs. Varnish Decision Chart
| Question | Go With… | Why |
|---|---|---|
| Is your project going outside or in direct sun? | Varnish | Offers better UV protection, especially spar or marine varnish |
| Do you want maximum durability and resistance to wear? | Polyurethane | More resistant to water, chemicals, and abrasion |
| Are you finishing softwood like pine or cedar? | Varnish | More forgiving and flexible on softer surfaces |
| Are you working on hardwood like oak or maple? | Polyurethane | Provides a harder, longer-lasting surface |
| Do you prefer a natural-looking finish? | Varnish | Has a warmer, more classic look with less plastic feel |
| Is fast drying and low odor important to you? | Water-Based Poly | Dries quickly and has fewer fumes |
| Will the piece be touched or used daily (like a table)? | Polyurethane | Better suited for high-traffic or high-use areas |
| Do you need something easy to apply and maintain? | Varnish | Easier to brush on and recoat over time |
A Video on Varnish
We’ve used plenty of videos on polyurethane but never used a video description devoted just to varnish, so today, we chose one for you.
It actually is pretty interesting, and we recommend you take 6 minutes to watch it. We guarantee you will learn something new.
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