Spar Urethane vs Polyurethane

Wondering what the difference is between spar urethane vs polyurethane? Then you’ve come to the right place!

We’ll go through the pros and cons of each wood finish a bit further down the article, but first, a property comparison table for those who want to quickly compare the two!

Spar Urethane vs Polyurethane At A Glance

Getting your head around all the different properties that each of these wood finishes provides can be difficult, so we’ve laid it all out in an easy to read table.

Here you will be able to quickly and easily compare spar urethane with polyurethane side by side.

PropertySpar UrethanePolyurethane
BasesWater and Oil BasedWater and Oil Based
Can be applied toWoodWood, metal, rubber
Dry TimeFastSlow
UV ResistantYesNo
Spray ApplicationNoYes
FumesLotsNot much
Can be degraded by chemicalsYesNo
Changes color over timeNoYes
Suitable for OutdoorYesNo

As you can see, there are a lot of different properties that spar urethane and polyurethane have that are important to keep in mind when choosing between them.

Now let’s get into an introduction and some more detailed information about these two wood finishes!

Spar Urethane vs Polyurethane – Introduction

Woodworking can be both a satisfying hobby and a profitable business. Coming up with beautiful designs to decorate your home or make your customers happy is a rewarding experience.

Whether it be fine furniture, hardwood floors, or outdoor decking, protecting wood with the right finish can go a long way towards enhancing it’s durability and long-lasting good looks.

Looking for the perfect finishing product online or at your favorite hardware store can be quite complicated and confusing. And you definitely don’t want to end up with the unappealing and destructive consequences of improperly finished wood surfaces.

With the myriad of choices of wood finishing products available, spar urethane and polyurethane have emerged as 2 of the most popular options.

Each has its advantages, disadvantages, and applications that are specific to different woodworking preferences.

What is Spar Urethane?

spar urethane
Example of Spar Urethane

Spar urethane is a type of synthetic varnish that was developed initially as a coating to protect the spars of a boat or ship, hence the name (if you’re not familiar, a spar is basically a long pole or mast!) It provided a protective barrier against water exposure and air moisture that can damage wood.

Nowadays, it has been increasing in popularity among DIY enthusiasts and woodworkers to use on doors, windows, and other exterior woodworks.

Spar urethane is available either as a water-based or oil-based product.

The water-based urethane dries faster and is more environment-friendly while the oil-based one is generally preferred for boats and tougher exterior jobs. It is also available in satin, semi-gloss, and gloss finishes.

Pros of Spar Urethane

Spar urethane is quite flexible and will not crack during the natural expansion and contraction of wood due to changes in humidity and temperature.

It is resistant to ultra-violet light, and will not darken over time.

It dries quite fast, as well.

It can be painted, wiped, or sprayed onto surfaces, depending on the dilution. It also produces minimal odors during application.

Cons of Spar Urethane

Spar urethane is flammable so extreme caution should be exercised during application.

It is also a thick and viscous substance that can be tricky to apply. It needs to be properly diluted especially when applying over a large surface area.

Its quick-dry property can also be a disadvantage, especially in warm weather, as it may dry out even before you can remove brush marks and create a smooth finish.

It is easily degraded by exposure to alcohol or harsh chemicals.

Spar urethane is also expensive, and the quality differs from one manufacturer to another.

What is Polyurethane?

Example of Polyurethane

Polyurethane is a synthetic polymer made from long chains of repeating molecules. It is designed to be strong and flexible, allowing it to move naturally with the material it is applied onto without cracking or flaking off.

Polyurethane is available both as a water-based and an oil-based product.

The water-based polyurethane dries faster, is easier to apply, and less smelly, making it a better option for indoor use.

The oil-based type is thicker, thus tougher, and needs fewer coats than the water-based one.

However, it is a bit trickier to apply, slower to dry and tends to darken over time which can eventually change the color of the wood.

Pros of Polyurethane

Polyurethane is not flammable so you can use it safely even near heat sources.

It dries slower so you have ample time to apply and work it into a smooth and polished finish.

It is resistant to most chemicals including alcohol.

It has a high degree of water, heat, and cold-resistance.

It provides a smooth finish not only on wood but on rubber and metal, as well.

It is quite affordable and is now available in ready-to-use spray cans.

Cons of Polyurethane

Polyurethane is not resistant to ultra-violet light, and prolonged exposure will degrade and shorten its lifespan.

It is less environment-friendly because of the fumes it releases when applied and during drying, therefore, ventilation is crucial. It also dries slower than spar urethane.

Although it produces a shiny and polished finish, it darkens and discolors as time goes by.

It is also quite hard to remove if you wanted to refinish your wood surfaces.

Care should be taken to ensure it is stirred before use and not shaken to prevent air bubbles from getting into your final finish.

The Differences Between Spar Urethane and Polyurethane

There are several points that we can use to compare and contrast these 2 products, and knowing about them may help guide you as to which one may be more suited to your needs.

Oil Content

Spar urethane contains more oils than polyurethane, making it more pliable and flexible.


Both products can be applied using a brush. You can use a standard bristled brush or a foam brush with polyurethane, but spar urethane requires a bristled brush only because of its thicker consistency.

They can also be applied by wiping using a clean, lint-free rag, but spar urethane will require dilution with mineral spirits, and will also need several applications because of the dilution process.

Polyurethane has a one-up over spar urethane as it can also be applied using a spray gun, and, as mentioned before, there are ready-to-use spray cans available already.

Drying Time

Spar urethane dries much faster than polyurethane, so if you want to finish projects faster, spar urethane is your go-to.

However, if you are still a beginner, or want to be as meticulous as you want in your wood finish, polyurethane is your best bet because of its slower drying time.

The downside? There is a higher risk that your project will get contaminated by dust and particles that can get stuck in the finish during the drying process.


Both products release fumes, but spar urethane is superior to polyurethane in this aspect.

Spar urethane releases less fumes, making it more eco-friendly compared to polyurethane.

It is strongly recommended, though, that whatever product you choose, proper ventilation, protective gear and clothing, and maintaining a clean workplace are strictly observed to prevent any accidents or injury.

Which One Should You Choose?

Spar urethane and polyurethane are both excellent products that can give you high-quality wood finishing.

To help you choose which is which, there are a few factors that you need to consider, including:

The Material

Both are excellent for wood, but polyurethane can also be used on metal and rubber, which makes it a versatile choice.

Indoor or Outdoor Use

Both products are waterproof and resistant to temperature changes. They are also both flexible enough to move with the wood naturally as it expands and contracts accordingly.

Spar urethane, however, contains additives that give it resistance to ultra-violet light that helps the wood maintain its color even during prolonged exposure to sunlight, making it more suitable for your outdoor projects.

Exposure to Chemicals

Polyurethane performs better than spar urethane when it comes to exposure to chemicals such as household cleaners and alcohol. This is highly significant if your wood surface is a tabletop or a bar counter that is regularly cleaned with chemicals.


Spar urethane is pricier, and the quality varies greatly as compared to polyurethane, although the ready-to-use polyurethane sprays cans tend to be more expensive than spar urethane because of the convenience.

Spar Urethane vs Polyurethane – Conclusion

We hope this article has helped explain the differences between spar urethane and polyurethane. Which one is better? It all boils down to the project you need it for, and the outcome you’re after!

Here are some related articles you may also enjoy:

Best Polyurethane for Floors
Best Water Based Polyurethane
Mineral Spirits vs Paint Thinner