{"id":368,"date":"2026-10-28T06:32:58","date_gmt":"2026-10-28T06:32:58","guid":{"rendered":"https:\/\/refshape.com\/blogs\/?p=368"},"modified":"2026-10-28T06:32:58","modified_gmt":"2026-10-28T06:32:58","slug":"insulating-bricks-explained-how-to-cut-furnace-heat-loss-without-weakening-your-lining","status":"publish","type":"post","link":"https:\/\/refshape.com\/blogs\/insulating-bricks-explained-how-to-cut-furnace-heat-loss-without-weakening-your-lining\/","title":{"rendered":"Insulating Bricks Explained: How to Cut Furnace Heat Loss Without Weakening Your Lining"},"content":{"rendered":"

The heat you cannot see is still costing you<\/b><\/h1>\n

Walk around a furnace that is running well and you will not see its biggest daily loss. There is no leak to point at and no crack to photograph. The heat is simply moving, slowly and steadily, through the lining and out through the shell. To hold the same temperature inside, the burner has to keep replacing that heat.<\/span><\/p>\n

That is why <\/span>insulating bricks<\/span><\/a> matter. The dense bricks facing the flame get most of the attention, because they take the wear. But the insulating layer \u2014 on the hot face in some designs, or behind the dense lining in others \u2014 decides how much of the heat you paid for stays where you need it.<\/span><\/p>\n

This guide explains, in simple terms, how insulating bricks differ from dense bricks, how they slow heat loss, how Refshape’s Xlite range is organised, and how to choose a grade without weakening the lining.<\/span><\/p>\n

Dense bricks and insulating bricks do opposite jobs<\/b><\/h1>\n

It helps to stop thinking of a lining as one material. A good furnace lining is a team, and each layer has a different job.<\/span><\/p>\n

Dense bricks are built for strength. They are heavy, hard and made to resist wear, abrasion, slag and direct contact with the process. But because they are dense, heat passes through them fairly easily. Used alone through the full wall, they hold up mechanically \u2014 and let a lot of heat escape.<\/span><\/p>\n

Insulating bricks do the opposite job. They are light and porous, and the trapped air inside them is what slows heat down. Their strength is lower, and they are not made to take heavy load, direct abrasion or aggressive slag on their own. Judging one type by the other’s strength misses the point of both.<\/span><\/p>\n

In practice, you layer them. The dense layer faces the process and takes the punishment. The insulating layer sits behind it, or forms a hot-face lining where conditions allow, and keeps the heat in.<\/span><\/p>\n

How insulating bricks actually save energy<\/b><\/h1>\n

Thermal conductivity is how readily heat travels through a material. A lower figure means heat moves through more slowly, so less reaches the outer shell. That is the basic reason an insulating brick saves energy \u2014 it makes the wall a poorer path for heat.<\/span><\/p>\n

There is one catch worth remembering. Conductivity is not a single, fixed number you can compare carelessly. It changes with temperature, so a figure measured at one temperature does not tell the whole story at another. When you compare two bricks, compare conductivity values measured on the same basis, and always relate them to the temperature your lining will actually see.<\/span><\/p>\n

Structure matters as well as the headline figure. Refshape describes its Xlite insulating bricks as specially formulated with independent pores for maximum insulating efficiency. Independent, closed-off pores help in two ways: they trap still air, which is what insulates, and they limit gas permeation through the brick. That is also why Xlite bricks are described as suitable for hot face insulation, since gas permeation is prevented. In simple terms, heat and hot gases find it harder to work their way through the wall.<\/span><\/p>\n

Position matters too. As backup behind a dense hot face, an insulating brick lowers shell temperature and heat loss. As a hot-face lining, it must also cope with temperature, atmosphere and contact at that face. The same brick can be sensible in one position and poor in another.<\/span><\/p>\n

The Xlite range, in plain terms<\/b><\/h1>\n

Refshape’s insulating bricks sit in the Xlite range. Read it as a family of grades, not one brick with one temperature, so you can match density, porosity and service temperature to the job.<\/span><\/p>\n

At the lower-temperature end, Xlite CF and Xlite HF suit backup layers and less demanding hot-face positions, where heat loss and weight still matter and conditions are well within their grade limits.<\/span><\/p>\n

The numbered Xlite grades \u2014 including Xlite 8, 10, 12 and 14, and Xlite 23, 26, 28 and 30 \u2014 cover higher service temperatures across the range. Refshape states that the Xlite range can be safely used for service temperatures up to 1650\u00b0C for hot face linings. Please read that carefully: it is the top of the range, not a promise that every Xlite grade is suitable at that temperature. Each grade has its own limit, and the grade you select must cover your actual hot-face temperature with a sensible margin.<\/span><\/p>\n

As you move through the range, the properties move together. A lighter, more porous brick usually insulates better but carries less load and resists abrasion less well. A denser grade is stronger but lets a little more heat through. That trade-off is normal \u2014 \u201clightest\u201d is not the same as \u201cbest.\u201d<\/span><\/p>\n

Start from the job, not the catalogue. Note the hot-face temperature, the load and the atmosphere, shortlist the Xlite grades that fit, and confirm the final grade against the current Refshape datasheet. That check protects you from the most common error here: a well-made brick chosen for the wrong duty.<\/span><\/p>\n

Choose by temperature, load and atmosphere \u2014 not temperature alone<\/b><\/h1>\n

Temperature is the first question, but it should never be the only one. Use the checklist below as a starting point for discussion with your refractory supplier, then confirm the grade for your exact furnace.<\/span><\/p>\n\n\n\n\n\n\n\n\n
Your situation<\/b><\/td>\nWhat to check first<\/b><\/td>\nTypical lining position<\/b><\/td>\n<\/tr>\n
Steel or heat-treatment furnace<\/span><\/td>\nTemperature, load, cycling<\/span><\/td>\nBackup behind dense hot face<\/span><\/td>\n<\/tr>\n
Cement kiln or preheater<\/span><\/td>\nTemperature, dust, alkali<\/span><\/td>\nBackup \/ selected hot-face zones<\/span><\/td>\n<\/tr>\n
Ceramic or glass furnace<\/span><\/td>\nTemperature, atmosphere<\/span><\/td>\nHot face or backup, by grade<\/span><\/td>\n<\/tr>\n
Boiler or incinerator<\/span><\/td>\nTemperature, gas flow<\/span><\/td>\nBackup insulation<\/span><\/td>\n<\/tr>\n
Petrochemical heater<\/span><\/td>\nTemperature, atmosphere<\/span><\/td>\nHot face or backup, by grade<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Think about the whole wall, not a single brick. Hot-face temperature, temperature at the back of the insulating layer, and target shell temperature are three different things. So is the atmosphere \u2014 alkali vapour, reducing gases or process dust can attack the lining, so gas permeation, chemical attack and thermal cycling belong in the decision too.<\/span><\/p>\n

Joint design and expansion allowance matter too. A good grade installed with poor joints will still lose heat through those joints and can crack or shift in service.<\/span><\/p>\n

Common mistakes that weaken a lining<\/b><\/h1>\n

The first mistake is using an insulating brick as if it were a structural, dense brick: putting it where it must carry heavy load, support the structure or take direct abrasion and slag. That is not a fault in the brick. It is a brick asked to do a job it was never designed for, and the lining pays for it.<\/span><\/p>\n

The second is choosing by price or by density class alone. A cheaper or lighter grade that is wrong for the temperature or atmosphere is not a saving; it is a relining waiting to happen. The third is comparing conductivity figures that were measured at different temperatures and treating them as if they were like for like. The fourth is leaving expansion and joints out of the plan, then blaming the material when the lining moves.<\/span><\/p>\n

All four mistakes have the same cure: specify the duty fully, and check the grade against it before you order.<\/span><\/p>\n

Tell us the duty, and we will help you match the grade<\/b><\/h1>\n

Layer insulating bricks with dense bricks, choose them by temperature, load, atmosphere and position together, and confirm the grade on the datasheet, and they will help you cut heat loss without weakening the lining that protects your plant.<\/span><\/p>\n

Refractory Shapes has been known for quality and reliability since 1973. If you are planning a new lining or a relining, send Refshape your furnace type, hot-face temperature, the backup temperature you are aiming for, the load and atmosphere, and the sizes and quantity you need. With that information, the team can help you shortlist an Xlite grade that fits the duty \u2014 instead of leaving you to guess from a catalogue.<\/span><\/p>\n

Note before publishing: Confirm the selected Xlite grade, its service temperature, density and thermal conductivity against the current Refshape datasheet for your furnace, load and atmosphere before ordering.<\/span><\/i><\/p>\n

Frequently asked questions<\/b><\/h1>\n

1. What is the difference between insulating bricks and fire bricks?<\/b><\/h2>\n

Fire brick is a broad term for bricks that resist high temperature. Dense fire bricks are strong and wear-resistant but let more heat through. Insulating bricks are a type of fire brick made light and porous to slow heat down. Most linings use both, in layers, rather than one or the other.<\/span><\/p>\n

2. Can insulating bricks be used on the hot face?<\/b><\/h2>\n

Yes, in suitable conditions. Refshape describes Xlite bricks as suitable for hot face insulation, since gas permeation is prevented, and says the Xlite range can be safely used for service temperatures up to 1650\u00b0C for hot face linings. That is the top of the range, so confirm that your specific grade covers your temperature, load and atmosphere.<\/span><\/p>\n

3. How do I choose the right density or grade?<\/b><\/h2>\n

Start with the service temperature, then add the load the brick must carry, any abrasion or chemical attack, and whether it sits on the hot face or behind a dense lining. A lighter grade usually insulates better but carries less load. Shortlist grades on those duties together and confirm the grade on the Refshape datasheet.<\/span><\/p>\n

4. Do insulating bricks really save fuel?<\/b><\/h2>\n

They reduce heat loss through the furnace wall by slowing how readily heat passes through the lining, so the furnace needs less energy input to hold temperature than it would with a poorly insulated wall. The actual effect depends on your furnace, lining design and operating pattern, so no single saving figure applies to every plant.<\/span><\/p>\n

5. What does thermal conductivity mean in simple terms?<\/b><\/h2>\n

It is how readily heat travels through a material. Lower conductivity means heat moves through more slowly, which is what you want from insulation. Because conductivity changes with temperature, compare values measured on the same basis and at a temperature relevant to your lining.<\/span><\/p>\n

6. What are Xlite insulating bricks?<\/b><\/h2>\n

Xlite is Refshape’s range of insulating bricks, specially formulated with independent pores for maximum insulating efficiency. The range includes Xlite CF and HF for lower-temperature duty and numbered grades such as Xlite 8, 10, 12, 14, 23, 26, 28 and 30 for higher service temperatures across the range.<\/span><\/p>\n

7. Can I replace a dense brick lining entirely with insulating bricks?<\/b><\/h2>\n

That is usually not advisable. Insulating bricks have lower strength than dense bricks and are not designed on their own for heavy load, direct abrasion or aggressive slag attack. A layered lining \u2014 dense where the process is harsh, insulating where heat loss matters \u2014 normally gives a safer balance.<\/span><\/p>\n

8. What information should I share when I enquire?<\/b><\/h2>\n

Share your furnace type, hot-face temperature, the backup or shell temperature you are aiming for, the load on the lining, the furnace atmosphere, and the sizes and quantity you need. That lets the supplier match an Xlite grade to the duty instead of quoting on temperature alone.<\/span><\/p>\n

9. Why does gas permeation matter in an insulating brick?<\/b><\/h2>\n

If hot gases can work their way through the brick, they carry heat with them and can affect the layers and shell behind it. Independent pores help limit that movement, which supports insulating efficiency and is one reason Xlite bricks are described as suitable for hot face insulation.<\/span><\/p>\n

10. How is an insulating brick different from castable insulation?<\/b><\/h2>\n

An insulating brick is a pre-fired, shaped unit with set dimensions, laid with joints as part of a brick lining. An insulating castable is a refractory material mixed, placed or cast on site and then dried and fired in position. The right choice depends on the furnace shape, access, lining design and shutdown plan \u2014 ask which suits your equipment.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

The heat you cannot see is still costing you Walk around a furnace that is running well and you will not see its biggest daily loss. There is no leak […]<\/p>\n","protected":false},"author":1,"featured_media":369,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[19],"class_list":["post-368","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-all-post","tag-insulating-bricks"],"_links":{"self":[{"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/posts\/368","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/comments?post=368"}],"version-history":[{"count":1,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/posts\/368\/revisions"}],"predecessor-version":[{"id":370,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/posts\/368\/revisions\/370"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/media\/369"}],"wp:attachment":[{"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/media?parent=368"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/categories?post=368"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/refshape.com\/blogs\/wp-json\/wp\/v2\/tags?post=368"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}