We often get calls asking “Do you have Firebrick?”.  The answer to that question in a broad sense is… “yes… we carry many types of Firebrick”.  But more specifically the answer is… “It depends on which Firebrick you’re looking for.” We thought we’d put together a brief overview on the most common types of Firebrick… Their qualities, their differences and their limits.

Usually when people call us looking for “firebrick” they are referring to one of the two most commonly used types of Firebrick.  Insulating Firebrick (IFB or “Soft Brick”) or Dense Firebrick (“Hard Brick”).


Insulating Firebrick (IFB or Soft Brick) is a soft, very light weight brick that does exactly what its name implies… It insulates.  The job of IFB is to reflect heat back into the firebox and it does so with great efficiency.  IFB have very low thermal conductivity… meaning they don’t allow heat to pass through… it actually reflects heat.  These bricks are soft and can be cut with a hack saw, drilled or routered with relative ease.  Which makes them ideal for custom shapes and trimming.  Most commercially bought pottery kilns are lined with IFB due to their outstanding insulating properties and ability to heat up and cool so quickly.

Dense Firebrick (Hard Brick) is a hard, very dense brick.  Dense Firebrick is not classified as “insulation”.  Although it can take the heat very well, even more heat than an IFB, it has a much higher Thermal Conductivity.  Meaning the heat will pass through, absorbing into the brick.  Instead of insulating the firebox, it will act as a heat sink, absorbing and radiating the heat.  This often will cause a firebox box to take longer to heat up (while the brick first absorbs the heat) and much longer to cool down (because the brick itself must dissipate the heat).  Because Dense Firebrick are so heavy, and durable they are a great option for structures that may see more abuse or direct flame.  Standard home fireplaces, outdoor firepits and woodfired pizza oven floors are examples of items usually constructed from some grade of Dense Firebrick.

Temperature Ratings & Sizes:

Insulating Firebrick (IFB or Soft Brick) can be bought in multiple temperature ratings and sizes.  Morgan Thermal Ceramics K23’s are the industry standard in IFB.  They have a 2300 degree continuous rating and are used in many industrial and hobby applications.  Also available is the K26 which has a 2600 degree continuous use rating but is more dense and doesn’t insulate quite as well as the K23.  So unless you’re going to be firing at the higher temperature… It’s most likely a better fit to use the K23’s.  Thermal Ceramics also makes a JM28 High Temperature IFB.  These have a 2800-degree use rating.  Other temperature ratings are available… But these are the most common.   K23’s, K26’s, JM28’s and all of the IFB’s available can be purchased in any number of sizes… But here at HTI we mainly stock these three types of brick in two standard brick sizes…  9” x 4.5” x 2.5” and 9” x 4.5” x 3”.  Which temperature rating and size you’ll need will be determined by your intended application.  Below are the links to the data sheets on Morgan’s IFB.

Higher Temp Rated IFB by Thermal Ceramics

Lower Temp Rated IFB by Thermal Ceramics

Dense Firebrick (Hard Brick) is also available in multiple sizes and grades.  Grades of Dense Firebrick are more commonly listed as “Low Duty”, “Medium Duty”, “High Duty” and “Super Duty”.  As the grades increase, the thermal conductivity and strength will also increase while the porosity will decrease.  This means that a “Super Duty” brick will be much stronger, and hold heat much better than a “Low Duty” brick.  Countless sizes are available in the Dense Firebrick but here at HTI we only stock two sizes of Harbison Walker’s “Super Duty” brick.  The first is commonly referred to as a “clipper”.  It’s a 9” x 4.5” x 2.5” hard brick with a temperature rating over 3,000 degrees.  We also stock a “split” of this same brick… which is 9” x 4.5” x 1.25” (referred to as a “split” because it’s basically the same brick cut in half).  As mentioned, other sizes are available… we just don’t stock them here.  So please don’t hesitate to call if you’re looking for something different.

Wrap Up

Insulating Firebrick (IFB or Soft Brick) and Dense Firebrick (Hard Brick) both have their uses in any high temperature project.  Even a well-insulated kiln built out of IFB could benefit from a floor using Hard Brick to save the abuse to the Soft Brick.  While IFB could not handle the rigors of a wood fired pizza oven.  Generally, if you want to build an insulated firebox for any purpose, IFB’s will be the best choice based on heat efficiency when abuse from direct flame and abrasion can be avoided.  If abuse, abrasion and direct flame cannot be avoided, a Hard Brick will most likely be your best option.

If you have any questions about what may or may not work in your application… Give us a call and we’ll see if we can help.