Spar Urethane vs. Polyurethane vs. Polycrylic: Their Differences

By MWB-Team •  Updated: 06/16/23 • 

Polyurethane, spar urethane, and polycrylic are three popular wood finishes. Although they all sound the same, all these are different finishes used for different purposes. In this article, we’ll walk you through each finish, their differences, and when to use each.

What is Spar Urethane?

Spar urethane is a wood finish designed to withstand different elements from extreme moisture, ultraviolet light, wind, and other elements. It is a spar varnish, but it includes urethane plastic as one of its binding resins, thus the name spar urethane.

Spar varnish was used on the ship’s spars to protect them from exposure to wind, moisture, sun, and other harsh conditions. It was formulated to resist all these extreme elements and still remain flexible in letting the wood expand and contract.

Minwax Helmsman Spar Urethane

Minwax Helmsman Spar Urethane

The most common type of spar urethane is oil-based, but there is also a water-based type. Spar urethane is a transparent wood finish, but it’s high in resins, which change the color slightly to a yellowish hue. It is also high in additives, making it great for dispersing ultraviolet light. This is one of the reasons it is a favorite for woodworkers using to finish outdoor furniture.

What is Polyurethane?

Polyurethane is a type of varnish that contains plastic resins, which form a hard protective plastic-like surface once it hardens. Poly is available in both oil-based and water-based versions. Oil-based polyurethane usually has more shine and is great if you prefer a warmer, amber tone it provides. Water-based polyurethane has a milky appearance but hardens to a clear finish on the wood. Check out our informative guide on water-based vs. oil-based poly.

Varathane Polyurethane

Varathane Polyurethane

Polyurethane is one of the most popular wood finishes because of its high protective seal it forms. It is a durable finish, easy to work with, and is more resistant to different elements such as water, solvents, and abrasion. Polyurethane is sometimes referred to as ‘liquid plastic’ because of the hard protective film it forms.

What is Polycrylic?

Polycrylic is a water-based clear finish from Minwax. It is used as a protective sealer for most indoor wood projects like furniture, desks, bookcases, cabinets, and trim. Unlike spar urethane and polyurethane, polycrylic should be exposed to minimal moisture, heat, and other elements. Polycrylic is not the best choice for wood surfaces that face extreme elements.

Minwax Polycrylic

Minwax Polycrylic

Polycrylic is only available as a water-based finish and is more environmentally friendly compared to spar urethane or polyurethane. It can be compared to water-based polyurethane, but it is less durable and only meant to be used on indoor wood projects. Polycrylic also has a milky appearance like water-based polyurethane and dries crystal clear.

Spar Urethane vs. Polyurethane

While spar urethane and polyurethane have very similar ingredients, the major difference is the ratio. With spar urethane, you have more oil compared to oil-based poly. More oil content in spar urethane makes it more flexible than oil-based polyurethane, so it is better for handling wood exposed to temperature and humidity changes.

The high oil content and better flexibility make oil-based spar urethane an excellent choice for outdoor wood projects. It can better resist elements like rain, temperature changes, snow, etc. Spar urethane is also high in additives that protect outdoor wood projects from harmful UV rays.

If you’re looking for the best polyurethane for outdoor use, check out our best exterior polyurethane.

Polyurethane vs. Polycrylic

While polyurethane and polycrylic are almost the same, there are some differences. Polycrylic is water-based and also tends to dry faster than polyurethane. On the other hand, polyurethane can be oil-based or water-based. Both water-based polyurethane and polycrylic look the same and dry to a crystal clear hard finish.

However, water-based polyurethane has more resistance to heat, water, or physical damage. Use polycrylic on wood surfaces that are not exposed much to elements such as heat, moisture, and foot traffic. These include shelves, side tables, and bookcases. Water-based polyurethane can be used on floors, furniture, tabletops, and other indoor wood surfaces.

Spar Urethane vs. Polycrylic

The major difference between spar urethane and polycrylic is their durability. Spar urethane is more durable and protects against extreme elements such as rain, UV damage, and temperature changes. They also have different appearances when fully cured, with polycrylic being crystal clear, while spar urethane enhances the beauty of wood and has a yellowish hue.

Spar urethane is great for outdoor projects because of its superior durability. polycrylic, on the other hand, is good for protecting indoor wood projects that will not be exposed to extreme temperature, heat, or moisture changes.

When to Use Each

Spar urethane, polyurethane, and polycrylic are good protective top coats for wood projects. However, each has pros and cons, making it suited for a different job. Before deciding on which to use, consider the location of your project, how you’ll use the wood’s surface, and exposure to different elements.

MWB-Team

Hello there! This is the Make Wood Better Team. Here, we share informative how-tos and guides focused on making wood better. Whether it's finishing wood, maintenance, or restoration, there's something on this website for you to learn and improve your skills.