Spar Urethane Vs Polyurethane: Which Is Better For Wood Finishing?

There are various types of wood finishes on the showcase, which serve specific functions for your DIY projects. Some widespread kinds include spar urethane and polyurethane. Although the names are similar, there are several differences between them.

If you are unsure about selecting an appropriate option, check out our article to take a closer look at the detailed comparison between spar urethane vs polyurethane. This blow-by-blow comparison helps you to choose the suitable choice to apply the proper coating for your furniture. 


Overview Of Spar Urethane & Polyurethane

What is spar urethane?

Spar urethane is a kind of synthetic varnish that is more durable and designed for marine use. Its purpose is to offer a firmly protective barrier against water exposure, wind, and air moisture damaging the wood. 

In addition, it is one of the common choices to apply the coating for exterior furniture, doors, windows, and sheds. Spar urethane is also the right pick for products that are exposed to direct sunlight. 

On the other hand, the standard requirement for a marine varnish is to protect boats against salt water, wind, adverse weather, and air moisture. Because of those typical requirements, spar urethane is a flexible item to help the wood withstand the exterior elements at ambient temperature. 

Besides, there is a water-based spar urethane, which is less widespread on the showcase. However, it is environmentally friendly because it discharges fewer fumes and dries quicker than other oil-based counterparts. As a result, it is a perfect option for those who want to complete DIY projects quickly and do not possess a well-ventilated workshop.


What is polyurethane?

Although both spar urethane and polyurethane are available in oil-based and water-based products, polyurethane is one of the most widespread substances. Polyurethane coatings are synthetic polymers, providing sturdy and flexible performance. 

Furthermore, related to the science aspect, polyurethane is a synthetic resin, which features as transparent in color and highly resists abrasion. It is resistant to mildews, water, and fungus, bringing durable outcomes for outdoor and indoor DIY projects. 

On the other hand, water-based polyurethane is an ideal choice for woodworkers concerned about the environment. It is safer to apply and releases fewer fumes than solvent-based and oil-based polyurethane. 


6 Main Differences Between Spar Urethane Vs Polyurethane

Although spar urethane and polyurethane bring optimal results and offer excellent protection for your furniture, each type has specific features. Thus, let’s check out some primary differences between spar urethane vs polyurethane to find out the suitable choice by yourself.

Application procedure

You can use a brush to apply both spar urethane and polyurethane. However, it is advisable to use a bristle brush when using spar urethane, while a foam brush is perfect for applying polyurethane. 

In addition, it is straightforward to apply spar urethane because it does not need many layers or coats to reach the shiny gloss. Meanwhile, applying polyurethane requires more techniques by carefully checking the application style and direction to avoid brush strokes and bubbles. 

Specifically, some woodworkers lay on a thinning method to form a smooth surface. Next, they stir polyurethane well to mix mineral spirits and the chemicals. It is tactical to avoid shaking the item because air bubbles may build up, visible in the final product. Nevertheless, this method requires multiple layers and applications. 

Besides, polyurethane is a suitable option for spraying, whereas the opposite is true for spar urethane due to its thick consistency. Therefore, buy spray cans and thin polyurethane with mineral spirits. 

Although this method can be an expensive investment, it brings you many benefits. It saves time and energy during the cleaning process and facilitates the procedure of applying the wood layers.

Learn more How to apply polyurethane here to receive the optimal results.


Oil content

The oil content that each of the items contains is one of the primary differences. Specifically, spar urethane has more oils mixed in than polyurethane, which brings more flexibility to the application. As a result, your furniture has a lower risk of flaking and cracking under adverse weather or temperature changes. 

Meanwhile, polyurethane includes a lower oil content, giving less flexibility than spar urethane. However, it also gives you excellent glossy polish when applying it correctly and sufficiently. 


Both spar urethane and polyurethane releases fumes. Nevertheless, the fumes that spar urethane discharges are less harmful than the ones its counterpart releases. In addition, it is advisable to wear masks during using these products and work in well-ventilated areas.

If you are concerned about health and the environment, it is best to choose water-based products to release fewer fumes. On the other hand, polyurethane is not flammable, while spar urethane is flammable. Therefore, always check the safety of your workplace and discharge the items carefully. 


Dry time features

Spar urethane is prone to have shorter dry times than polyurethane. Thus, it is an ideal option for woodworkers who don’t have much time and want to use their finished products as soon as possible. Furthermore, it pays to check the number of coats to obtain the best outcome. 

Most woodworkers find it sufficient to do two coats of polyurethane to bring excellent protection for your furniture. On the other hand, spare urethane tends to dry by exposure to airflow or oxidation faster. Thus, if you set a fan near your furniture and work in air circulating areas, you boost the performance and speed up the drying process with ease. 

Meanwhile, polyurethane dries slowly, which needs a lot of time to pass. In addition, applying it in a highly humid workplace and cold air slows down the drying time, which is the most troublesome downside. Due to the slow drying process, it is best to check your projects frequently to avoid the potential risk of particles and dust penetrating in the finish. 


Advantages and disadvantages

Spar urethane is an ideal option to apply for exterior surfaces that are exposed to harsh conditions, such as adverse weather. It also releases less harmful odors and has a low level of toxicity, which is suitable for use in small or medium areas. 

In addition, one of the outstanding characteristics is the UV blockers, which bring excellent durability to prevent yellowing of the surface, fading, wear and tear as time goes by. It also resists water, appropriate for boat finishing.

However, spar urethane is susceptible to alcohol and chemicals. The finish can be downgraded when you use harsh chemicals to clean the surface. It is flammable, which is not advisable to use near heat sources like heaters or stoves.

Meanwhile, polyurethane brings a satin-like finish thanks to its slow drying process. As a result, woodworkers have more time to adjust mistakes and produce a smooth surface on the DIY project. It is also available in spray bottles, which gives more convenience to use in small corners of the product. 

Furthermore, it is straightforward to apply to rigid objects, such as metal and rubbers. Polyurethane is more resistant to harsh chemicals than its counterpart. In addition, it is not flammable, which is safe to apply near heat sources. 

Nevertheless, one of the most troublesome downsides is the pungent odors that polyurethane releases during application. Thus, wearing masks and working in well-ventilated areas is best to avoid potential health risks, such as headache, dizziness, and trouble breathing.

Besides, it is vulnerable to UV rays, making the outdoor furniture darken with time. Bubbles may build up on the final coat when polyurethane is not stirred well.



When it comes to the price of spar urethane vs polyurethane, there are several factors to consider. Firstly, spar urethane may change in quality depending on various manufacturers. However, it is prone to be more expensive than polyurethane. 

Meanwhile, polyurethane is more affordable, yet it is pricier when buying it in ready-to-use spray cans. Nevertheless, some woodworkers prefer to purchase this form because it is easier and more convenient to apply.

Spar Urethane Vs Polyurethane: Which Is Better?

Although there are some primary differences between Spar urethane vs Polyurethane, each wood finish offers you outstanding features. To sum up, spar urethane is the winner thanks to its ease of application, less harmful odor, and fast-drying time. 

In addition, it has a high level of oil content, bringing excellent flexibility. It is suitable for outdoor and indoor furniture because it is resistant to UV rays. Therefore, applying spar urethane increases your DIY item’s lifespan with ease.  


We hope you can select the most suitable product for your wooding finish process with this thorough spar urethane vs polyurethane comparison. Before buying any products, it pays to consider some factors such as application process, level of fumes that the wood finishing product emits, and drying time feature. 

Thank you for reading. Don’t hesitate to comment below if you have any follow-up ideas to gain more experience applying these products. Furthermore, please share it with your friends and relatives to learn more helpful tips for using spar urethane and polyurethane.