Varnish vs Polyurethane: What Actually Matters

Choosing between varnish and polyurethane has gotten complicated with all the conflicting information flying around. As someone who’s used both extensively on furniture, cabinets, and outdoor projects over the past fifteen years, I learned everything there is to know about when each one makes sense. Today, I will share it all with you.

The short version? They’re more similar than different, but the differences matter depending on your project. Let me break this down the way I wish somebody had explained it to me when I was starting out.

What’s Actually In the Can

Varnish is the old-school option — resins, oils, and solvents that combine into a hard, clear protective film when dry. There are a few flavors worth knowing about:

• Oil-based varnish: Made from natural oils like linseed or tung oil. Durable, brings out the grain beautifully, and has been used for literally centuries.
• Water-based varnish: Lower fumes, dries faster, more environmentally friendly. I’ve been reaching for this more often lately.
• Spar varnish: Has UV protectants built in. This is what I put on anything going outdoors. My porch rocking chairs have had spar varnish on them for five years and they still look great.

Polyurethane is the newer option — a synthetic resin finish known for being tough as nails and highly water-resistant. Two main types:

• Oil-based poly: Adds a warm amber tone, extremely durable, takes about 24 hours between coats. My kitchen table has this and it’s survived years of daily abuse.
• Water-based poly: Dries clear, fast-drying, low odor. Great when you don’t want to alter the wood’s natural color.

How They Go On

Probably should have led with this section, honestly, because application is where most people make their decision. Both can be brushed on, but the experience is different.

Varnish is pretty forgiving with a brush. Each coat needs overnight to dry, and you’ll want to sand lightly between coats for a smooth result. I find the application almost meditative — there’s a rhythm to it once you get going.

Polyurethane can be brushed, rolled, or sprayed. Oil-based poly also needs about 24 hours between coats, similar to varnish. Water-based poly though? I can get three coats done in a single day if I start early. That speed advantage is real when you’ve got a deadline or just limited patience.

Sand between coats regardless of which product you’re using. I use 320-grit for this — just enough to give the next coat something to grab onto without cutting through what you’ve already laid down.

Which One’s Tougher?

This is where polyurethane really pulls ahead. Oil-based poly forms a harder, more scratch-resistant film than traditional varnish. That’s what makes polyurethane endearing to us furniture builders who want our pieces to survive real life — not just sit in a showroom.

Varnish offers good protection against moisture and UV rays, which makes it the better choice for outdoor pieces. But for indoor furniture that’s going to take daily use — dining tables, kitchen cabinets, hardwood floors — polyurethane is tougher.

Water-based poly is slightly less durable than oil-based, but the gap has narrowed a lot in recent years. The newer water-based formulas are genuinely impressive.

How They Look

This matters more than people realize. Oil-based varnish and oil-based poly both add warmth — that amber glow that looks gorgeous on darker woods like walnut and cherry. On lighter woods, that amber tone adds depth and richness.

Water-based versions of both stay clearer and won’t yellow over time. I use water-based finishes on maple, birch, and ash specifically because I don’t want to change their natural color. The clarity is really noticeable on those light-colored species.

Over time, oil-based varnish can darken slightly with light exposure. Some people love that aged look; others find it annoying. Depends on the project and your taste.

The Maintenance Side

Both are pretty easy to maintain day-to-day. Damp cloth, mild soap if needed, done. The difference shows up over time.

Varnished outdoor pieces will eventually need touch-ups or recoating, especially if they’re getting direct sun and rain. I refinish my porch furniture every two to three years.

Polyurethane finishes on indoor pieces can go years without any attention. My kitchen cabinets have had the same poly finish for eight years and they still look good with nothing more than occasional cleaning.

The Environmental Angle

Both oil-based products have higher VOC levels — that strong chemical smell that lingers for days. If you’re working in an attached garage or a basement shop like I do in the winter, this matters.

Water-based products have significantly lower VOCs. Still want to have ventilation, but you won’t be hot-boxing your house with fumes. This is a real quality-of-life consideration that I didn’t appreciate until I switched my shop from detached garage to basement.

So Which One Should You Buy?

Here’s my honest take after years of using both:

Going outdoors? Spar varnish. Nothing else handles UV and weather as well.

Indoor furniture that needs to survive daily use? Oil-based polyurethane. Toughest option available.

Light-colored wood where you want to preserve the natural look? Water-based poly. Stays clear, dries fast, low smell.

Want that traditional, warm furniture-store look? Oil-based varnish or oil-based poly will both get you there.

Budget tight? Oil-based products of either type are generally cheaper per can. The longer drying times are the tradeoff.

The truth is, both products work well when applied properly. The “wrong” choice is usually just a slightly less optimal one, not a disaster. Pick the one that fits your project and your working conditions, apply it carefully, and you’ll get good results.