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Designing cast iron skillets has made us fanatical about seasoning: we’ve tried everything from perennial internet favorites to trusted family techniques, and ended up designing a custom seasoning oil blend for everyday cast iron care. In short, choosing the correct seasoning oil and process makes a big difference in the long-term condition of your pan.

Here’s what we’ve learned:

Applying Seasoning Oil to a well used Field No.10 First Casting.

Look for polyunsaturated fats

The most important word to remember about seasoning oil is “polyunsaturated.” These are the fats in cooking oil that convert to seasoning through a chemical reaction called polymerization. When selecting a seasoning oil, you want one that’s high in polyunsaturated fats and has a high ratio of polyunsaturated fat to monounsaturated fat.

Among common cooking oils, grapeseed oil and sunflower oil stand out for their high polyunsaturated fat content and desirable ratio of polyunsaturated to saturated fat. These are types of oil we selected for the Field Seasoning Oil blend, and our oils offer a bit more than what you’ll find at the grocery store.

How we made Field Seasoning Oil

Our optimized cast iron seasoning oil blend includes organic grapeseed oil and organic linoleic sunflower oil, both high in polyunsaturated fats and well-suited for seasoning, plus beeswax to keep the blend stable in the tin and on your pan. Both oils are neutral, meaning they won’t create strong scents or add noticeable flavors to your food.

We’ve long advocated for grapeseed oil — it’s what we use to pre-season every Field Skillet — and our Seasoning Oil is made with organic, cold-pressed grapeseed oil that you aren’t likely to find on the shelves: most supermarket grapeseed oils aren’t organic, and some less-expensive varieties are produced with undesirable chemical refining processes.

Sunflower oil is also high in polyunsaturated fats, and has similar cooking properties to grapeseed oil. Again, ours is a bit different than the brands at the supermarket: we use organic linoleic sunflower oil, a variety whose chemical composition — specifically, the positioning of double carbon-carbon bonds — is particularly suited to polymerization. Most store brands are high oleic sunflower oil: still great for high-heat cooking, but less effective for cast iron seasoning.

To land on our final blend, we tested these oils in a variety of proportions and optimized for seasoning performance, first and foremost, as well as neutral scent, texture, and ease of application. Use Field Seasoning Oil after every meal, and watch your skillet’s condition improve.

Pass on the flax

If you’ve been searching the internet for seasoning methods, you’ve likely come across flaxseed oil recommendations. Flaxseed oil belongs to a category of “drying oils,” which are known for their ability to polymerize when exposed to oxygen. Polymerization = good, right? Not in all cases.

Flaxseed oil does convert to seasoning readily — almost too readily. When heated, flaxseed oil will quickly produce a dark patina due to its low smoke point 225°F (compared to grapeseed oil at ~400-420°F). A skillet seasoned with flaxseed oil may appear perfect, but the seasoning flaxseed oil produces is often brittle and prone to flaking — especially when applied in consecutive coats. It looks great hanging on the wall, but won’t stand up to regular cooking.

And if you’re still on the fence, there’s this: while you can purchase food-grade flaxseed oil (non-food grade varieties are called linseed oil), drying oils are better known for their application in wood finishes than, say, roasted cabbages. We prefer to season our cookware with something we’d be comfortable cooking with.

What about butter, shortening, lard, and bacon grease?

Ask anyone with an heirloom cast iron skillet, and they’ll say that Grandma’s secret was bacon grease, lard, or cornbread with lots of butter. Those cooking fats probably made Grandma’s food tasty, but they weren’t the reason her pan was well-seasoned — more likely, the pan was in good shape from regular use.

Animal-derived fats like bacon grease and butter are high in saturated fats and low in polyunsaturated fats, a mix that won’t easily produce resilient seasoning. If you were to coat a skillet with bacon grease and bake it at 400°F for an hour, you might produce some dark (burned) residue, but very little seasoning, if any. Cooking fats with a higher ratio of saturated fats — a group that includes coconut oil, in addition to most animal-derived fats — are useful as a post-cleaning finish to protect your pan, just don’t expect them to produce any new seasoning.

What about other cooking oils?

The best way to season your skillet is simply to use it — the more frequently the better. Every time you heat oil in the pan, you build new layers of seasoning and strengthen your existing coating. But don’t reach for a specific oil when you’re cooking just because it’s good for seasoning your pan; choose the oil that best suits the dish you’re making, and know that your pan will be a little bit better-seasoned after.

Common cooking oils like olive oil will gradually produce seasoning, but won’t be as effective as grapeseed oil. Canola, other vegetable oils, and shortening are a little better. Coconut oil won’t do much at all. For best results, cook what you like and follow up with Field Seasoning Oil after cleaning.

How to use Field Seasoning Oil

A well-seasoned skillet will deliver non-stick performance and clean up with just a quick wash. Apply a dab of Field Seasoning Oil after cleaning to protect your skillet and build durable non-stick seasoning.