Your Pyrex Pan Actually Isn't the Best Pan for Baking Brownies

Here’s what you should use instead for the best-ever brownies.

Two square pans of brownies--a glass pan on the left and metal on the right--shot from overhead

Sara Haas, RDN

Have you ever made a batch of brownies and wondered, “should I be using a metal pan or a glass pan for this?” Whether you’re baking a batch from a brownie mix, putting an over-the-top spin on said mix, or making a classic brownie recipe like our Best Brownie or a pan of blondies, we have the answer and the reason why one pan is always the better option (unless your recipe says otherwise) when making brownies. 

First, remember that baking is a science.

There are plenty of factors that go into making a perfect batch of brownies. Since baking involves quite a bit of science, you can be confident that measuring your ingredients properly, ensuring your oven is at the proper temperature, and combining ingredients in the correct order, matters. But one of the possible places for error you might not be thinking of is your pan choice.

Is a metal pan or glass dish better for baking?

Is there really a difference in the two materials when it comes to baking? The answer is yes! Thermal conductivity–how quickly a pan heats up and cools down–is the reason metal works better than glass for baking, according to the Nordicware Test Kitchen. Metals, specifically aluminum (which is what many baking pans are made of), heat up quickly, allowing batter to rise, bake, and crisp up at a uniform pace. This, says Martin Philip, author and baker at King Arthur Flour, results in an evenly-baked, perfectly moist batch of brownies. Aluminum is also lightweight, says Philip, making it easy to transfer from countertop to oven–and if you’re clumsy, no worries, metal won’t break easily. 

Glass, on the other hand, has a low thermal conductivity,and is an insulator, according to the pros at Nordicware. This means it takes longer than metal to heat up, but it also holds heat longer than a metal pan. Because of this, brownies baked in a glass pan will need more time to bake. That slow heat-up and additional time can result in brownies with hard, overly-baked edges and a questionably “done” center. Glass can also be a bit heavy and cumbersome and unlike metal, can break when dropped.

Does this mean that you should ditch all of your glass pans? No way! For some recipes, a glass pan is a fine choice. That slow heat transfer makes them a great option for casseroles, lasagnas, and other dishes where there isn’t a need for precise, even heating. And because they retain heat longer than metal, they’re also perfect for serving, keeping food warm while it sits on the dinner table. 

Does a metal pan bake better brownies than glass? We conducted a test to find out.

To test the theory that metal pans perform better than glass pans for brownies, we baked two batches of Mmm-Mmm Better Brownies. We made one batch in a glass 9-inch square Pyrex pan and another batch using a metal (aluminum) 9-inch square baking dish. We baked each for 30 minutes as directed in the recipe and had a clear winner.

Two brownies, side by side, on the left, much shorter (baked in glass), and on the right much fluffier (baked in. metal)
The results of our brownie bake test, with the glass-baked sweet on the left and the metal-baked treat on the right.

Sara Haas, RDN

After 30 minutes, the brownies baked in the metal pan were perfect. The edges were slightly crisp, and the brownies were baked throughout, but still deliciously moist and tender. The brownies in the glass pan, as predicted, were cooked and mostly firm around the edges, but the middle was completely raw and inedible. The obvious solution was to increase the baking time for the brownies in the glass pan, which we tried on another batch, resulting in an additional 10 minutes of baking. The finished product had the edges that were crisp to the point of burning, leaving only the middle area as a desirable choice to eat. 

The Bottom Line

If you make brownies or bake often, consider using or purchasing a metal pan to use in place of your Pyrex dish. Metal pans, specifically aluminum, absorb and transfer heat more consistently than glass, making them perfect for delicious, evenly-cooked, moist  brownies every time. Metal pans are also excellent for other baked goods, like quick breads, cakes, cookies, and biscuits. But don’t toss your Pyrex. Save it for casseroles, stratas, lasagna, and other similar dishes. 

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