View Full Version : The Insulation Values Of Different Materials

David Paterson
10-17-2004, 01:15 PM
I decided to gather together this data in response to the recent discussion on the use of alternate fuels to run a glass studio.

My occassional sarcastic comments on that issue were based on the fact that I have yet to see a technology that I could readily put to use, and on my belief that good design using conventional fuels and known technology can gain as much if not more than 'cheaper' fuels using technology that has unknown variables and problems.

I believe electric furnaces in particular, where all the energy can be contained in a small unit that is sealed when not in use, can yield results equal to if not better than 'alternative technologies'.

Heat loss is a combination of the insulation value of the material, the square footage of the outside walls, and the leakage around doors, etc.

In a well designed electric melter, with the interior space only slightly larger than the crucible, and using the best insulation materials, the actual energy use would be substantially lower than a furnace that used waste oil that fired into a large firebox (creating perhaps 3X the interior volume), and that was insulated with higher density castable to take the extra abuse.

Replacing Kastolite 30 with 2600F IFB would cut the heat loss almost in half on its own. Replacing 6 lb fiber with Skamol board would gain another 30%. The Skamol is also very cheap. Cutting the interior volume in half or more would also drop the heat loss substantially.

I have edited this post to add the figures for one of the Microporuos Insulation products from Thermal Ceramics, BTU Block Board.

Here Are The Insulation Values Of Different Materials

Insboard 2600 HD Fiber Board
26 lbs/cu.ft.


Skamol SUPER-1100 E Calcium Silicate Insulating Board
15.3 lbs/cu.ft.


Thermal Ceramics Microporuos Insulation
BTU-Block Board
18 lbs/cu.ft.


Inswool HP Blanket

6 lbs/cu.ft

8 lbs/cu.ft.

G-26 LI Insulating Firebrick
48 lbs/cu.ft.


Kastolite 30 LI
90 lbs/cu.ft.


Mizzou Castable
139 lbs/cu.ft.


Greencast 94
163 lbs/cu.ft.


Franklin Sankar
10-17-2004, 05:43 PM
Do you have to ridigize the the micropore fibre ?

Henry Halem
10-17-2004, 08:06 PM
Microporuos is the heading of the line of insulating materials sold by Thermal Ceramics. It is an insulating material unlike any other type of material any of us are used to. The subheading that is applicable to us is the line called Flexible Min-K._Specifically you will look at the MIX F150 and MIX F182. You can find it at the following link. Oh yes Franklin, no don't rigidize it.

Microporuos (http://www.thermalceramics.com/products/categories/minkmicroporous.asp)

David Paterson
10-17-2004, 11:26 PM
I edited my original post to include the figures for one of the Microporuos Insulation products from Thermal Ceramics, BTU Block Board.

It seems fairly pricey:


So I was wondering if Henry, or anybody else has any direct experience with it. The heat loss figures are about a third of the Skamol Board, which had been the best of the lot. The question is whether the incredible heat loss figures actually work in practise.

You can download a data sheet about it and other Thermal Ceramics products here:


Donovan Brooke
10-18-2004, 12:24 AM
David, thanks for this post... good points to consider.


Henry Halem
10-18-2004, 09:20 AM
Yes I believe the heat loss figures put out by TC are accurate. We use about 1/2 inch on the crown of the EZtherm furnace and considering it in other locations as well. You have to be careful though where you put it as it max's out at about 1800 deg. F. so you do not want to put it in any area that gets to that temperature, directly on furnace crowns, etc. We now use it as the last layer of our crown. It is my belief that in some situations the energy savings $$$$$ will more than pay for the upfront cost. It is fragile to the degree that one should handle it carefully. It is the type of material that does not bend easily although it will somewhat. It is best used in flat crown or wall situations. The space saving from standard fiber is terrific.

Edward Dluzen
10-18-2004, 10:24 AM
Additionally there is from Zicar

MICROSIL Microporous Insulation

Max Use Temp 1742F

68F .132
392F .145
752F .173
1112F .208
1472F .263

Alumina Mat

Max Use Temp 3002F

315F .50
1000F .77
1400F 1.03
1796F 1.33
2192F 1.65
2597F 2.15

Alumina Blanket Type AB & MB

Max Use Temp 2912F

599F .50
1000F .70
1400F .90
1796F 1.25
2192F 1.60
2597F 2.15

Alumina-Silica Blanket Type ASB-2300 & ASB-2600

Max Use Temp 2300F and 2600F

Bulk Density of 4 pcf

500F .56
1000F 1.13
1500F 1.96

Bulk Density of 6 pcf

500F .45
1000F .94
1500F 1.70
2000F 2.80

Bulk Density of 8 pcf

500F .39
1000F .78
1500F 1.31
2000F 2.02

Bulk Density of 10 pcf

1000F .73
1500F 1.17
2000F 1.72

Alumina Insulation Type ZAL-15 & ZAL-15AA board

Max Continuous use 2822F & 2732F

482F .40
977F .60
1472F .90
1967F 1.30
2282F 1.70
2462F 1.80

Alumina-Silica Insulation Type AXL Board

Max Continous Use 2300F

752F .80
1472F 1.20
2012F 1.50

Alumina-Silica Insulation Type AXHTM Board

Max Continous Use 2600F

752F .60
1472F 1.00
2012F 1.70

There are a few more if anyone is interested.


Edward Dluzen
10-18-2004, 10:28 AM
Now we need to compare material cost vs savings in energy/payback time for the more expensive but better insulations.


Edward Dluzen
10-18-2004, 10:47 AM
There is a program


That is a neat program you have to pay for it, but it looks interesting, for calculating cold face temperatures of various materials layered or not.

There is a free sample running download.

Has anyone used this program? Or seen it?

I am not affliated with this in any way, unless I can get one for free.....


David Paterson
10-18-2004, 11:43 AM
One issue in designing furnaces for minimum heat loss is the following issue:

If you replace 6" of Kastoloite 30 with 3" of IFB which has one half the heat loss, is this a break even situation?

Logic would say that since the Kastolite furnace is much larger on the outside, the larger radiating area would loose more heat. But how much more?

The issue becomes important when you look at using an expensive product like the microporous insulation in place of several inches of 6 lb fiber, which is very cheap.

Does anybody have either theoretical or practical knowledge on this issue? If you spend a lot of money on high tech materials, are you just saving space, or is there substantial real savings on energy consumption?

David Paterson
10-18-2004, 12:07 PM
In regard to Zircar products, they are usually quite pricey.

The Thermal Ceramics BTU-Block Board works out to $13.90 per sq ft for one inch thickness from this website:


The Zircar Microsil Microporous Insulation works out to over $25.00 per sq ft in one inch thickness from the Zircar website:


Franklin Sankar
10-18-2004, 12:22 PM
Please allow me to tell a story related to your post.
I just got a piece of grey boad and was told that it is silicaboard and the btu/ft hr deg F is .11 at 1832 F. That sounds too good to be true. Is that posible. Any guesses what it is?
They are building a new plant and I get to wallow in the garbage, found some scraps no specs and no one will say what it is.
Its a pig delight now to find some ears to show Pete.

Is there such a thing as silica board that can go up to 2300F?


Ed Skeels
10-25-2004, 11:56 AM
An online application is available on the Harbison Walker website to calculate heat loss. You need to register and wait for a password. Its free. Image of results form below.

David Paterson
10-25-2004, 01:11 PM

Where exactly on the Harbison Walker website is the program to calculate heat loss?


Pete VanderLaan
02-20-2012, 06:20 AM
I have resurrected this thread at the request of Tom Clifton and it does seem chock full of stuff. I have made it sticky in "
Antiques and Classics" which I am not going to do here. Read away, and thanks Tom. I would take note that all of the reference data sheet links don't work at all.

Michael Love
09-04-2012, 06:42 PM
I am lazy, I don't want to take the time to learn how to calculate cold face temps, but I may have to. My wire melter is hot to the touch. I want to remove some of the frax blanket and replace it with microporous insulation. A shell temp of 100 would be nice but I may be dreaming. How much blanket do I need to get from the 2450 of the hot face down to the 1100 the microporous can deal with? The hot face is not normally 2450 but if the controller goes wild it will be that hot when kanthal melts and I do not want a meltdown to ruin the $$$ microporous.
So I ask the voices of experience - how many inches of frax between the heat and the microporous?

Dave Bross
09-05-2012, 05:09 AM
I'm going to suggest a different approach.

Get/make (twist the wires together on some K thermocouple wire, tape this to a glass rod or other non conductor) a handheld thermocouple probe and something to read the temp.
A lot of cheap multimeters will read K thermocouples now, or, in my case I use old controllers that have fried on the control side but still read temp.

start probing to see what temps you've got.

Too high? add more frax, check again.

Guaranteed results...because you know what temps you have for sure.

This is like batching/melting. Every furnace will be different due to age of refractories, tightness of assembly etc. etc.
What might work on mine may not work on yours.

This actually is the lazy way to do it because you eliminate a number of furnace teardowns and mistakes on how much insulation to order...or frying that high dollar insulation because your calculations weren't accurate.

Why not use block mix instead of high dollar insulation?


Pete VanderLaan
09-05-2012, 05:24 AM
Since you don't say how much fiber there is on the furnace now, it's hard to say whether you need more but given the various manufacturers it's safe to say it isn't enough. Putting microtherm on a wire melter is like putting Pirelli tires on a ford Taurus. Dave has a good point.

Just strip off the metal on the wire melter and wrap it in 8lb density fiber until you have at least four inches of fiber. More if you can. Cheaper and easier.

Your wire melter is never going to get to 2450F Your elements are going to fail way before that.

Dave Bross
09-05-2012, 10:01 AM
My little melters have about 4-5" of frax on them (outside of the firebricks holding the elements) and they're just slightly warm to the touch.
Nothing else for insulation, other than the tile board used to contain the frax, which doesn't really count.


I'll second Pete's estimate of what it would take for a quick, all frax fix.

Combo insulations will require the experimentation.

Michael Love
09-05-2012, 10:42 AM
I just built a new smaller furnace for color. It is in its second heat cycle. Having survived the trip to 2300 empty it is now cooling from 2300 with an empty pot. It has 20 Ohms of 13ga wire supported in grooves in 9 castolite slabs. The castolite is 2+ inches thin and the grooves are almost an inch deep so the slabs contribute almost no insulation. The chamber is just big enough for a pot the size of a large assay pot. Around the castolite I have 2 inches of 2600 and 5 more of 2300 blanket, then a pretty stainless shell. The controller is an inexpensive Fuji with a generic 35Amp 240V phase angle SCR. For safety there is a MDR and a door switch. Until I know that the whole project is not a monumental failure I will stick to the cheap assay pot and a type K thermocouple. I won't even buy any color chemicals till I see that it can make glass.
I don't yet know how well it can heat the glass load or how well it can recover from door opening but for now the process temp matches the control temp at a 100/hour right up to 2300.
So far so good, except that the shell is too hot to rest my hand on for more than a second or two. In Philadelphia we pay a lot for electricity and a hot shell looks like wasted money. I could just wrap more blanket around it but then it will be a long reach to the door in the top and I will have to make a new base and shell. Plus space in the shop is at a premium. I would rather remove some blanket and add some super insulation. I only need about 16 sqft and Thermodyne quotes 1in panels at $10.55/sqft.
I could just blindly remove 1 inch of blanket and replace it with microporous but I don't know what the temp of the hot face temp of the microporous would be since the temp at the 6in layer will rise as insulation is added.
I like Dave's suggestion of wrapping it with an excess of blanket then probe the layers to find a safe heat.
I hoped somebody would chime in with some comment like
"5 inches of 8lb blanket keeps my microporous happy"
"if you are at 2000, an inch of blanket will bring it down by x00
if you are at 1500, an inch of blanket will bring it down by y00
or some other bit of wisdom that could save this lazy guy from working - or worse - studying to find the answer.
>>Pirelli tires on a ford Taurus.
Our family taxi is a '99 Toyota Camry (Tarus equivalent) with Pirelli tires, Tokico shocks, Eibach springs, 190hp V6 and 5sp stick. Respect the lowly taxi, respect the lowly wiremelter.

Dave Bross
09-05-2012, 12:51 PM
What you have should be more than enough frax if I'm reading it right...as in 7" of insulation?

Something is very wrong if you can't put your hand on it.

All that comes to mind is that using Castolite instead of insulating firebrick to hang the elements may be contributing to the problem.

Another thought would be that something other than a metal shell might help.
Metal is very conductive of heat.
I have some distant memory of someone logging temp differences and finding the metal hotter than the frax in front of it...radiant vs. transmitted heat? I don't really remember..
Perhaps cast up some block mix panels for the exterior or use some tile board as an experiment for that.

As far as the quick fix...

I would be surprised if anyone here has used microporous on a furnace, or knows the temps. Hopefully I'm wrong.

As far as:

"if you are at 2000, an inch of blanket will bring it down by x00
if you are at 1500, an inch of blanket will bring it down by y00

Those numbers will be exclusive to your unit...just like with what you have, it shouldn't be that hot...local phenomena need specific local knowledge to unravel.

Like the aliens say having abducting you..."It's time for the probe!"


Good you're a car guy...you're in much similar company.

Michael Love
09-05-2012, 09:07 PM
I cranked it back up to 2300 and attacked it with a spare thermocouple, a digital voltmeter, and a type K lookup table. There is something wrong in the hottest few inches of frax, red heat too far from the core. No quick fix there, take it apart and figure out what I did wrong. Maybe I confused an old down quilt with a frax blanket.
Between the shell and the frax I measure 180F, one inch toward the heat I measure 475F. 4 inches in from the shell (or 3 inches out from the castolite) I see red heat - that can't be right.
Looking on the bright side - I found a heat flow calculator on a microporous site that claims I can lower the shell temp to 97F by replacing the last inch of frax with microporous, or even lower if I can fix the whatever is wrong deep inside.
Maybe I should rip it apart while it is glowing hot, the problem would illuminate itself to the naked eye.

Steve Stadelman
09-06-2012, 12:23 AM
180f on a steel shell on a little melter is pretty damn good. Don't over think this.

Pete VanderLaan
09-06-2012, 04:40 AM
Also, when you don't give out enough information in the first place, you shouldn't be surprised if you get an incomplete answer. You were the one who said you were too lazy to do the calculations . Insulation is deceptive stuff.

Dave Bross
09-06-2012, 04:58 AM
I suspect the Castolite is transferring a lot more heat than insulating firebricks would.
Look at how tight the joints are between the slabs of element hanger too.

Agree with Steve..that's not too bad at the shell temp wise. Don't get too crazy here.

It's going to need a rebuild/elements soon enough once you start melting glass with it.

Run it like it is with maybe a bit more insulation around the outside (if you must) and change the internals to insulating firebrick on the first rebuild. Also spray/paint the firebricks with the RFC 17 mentioned here:


It will make the brick last a lot longer and does help a bit with slowing down heat transfer.

You could log the energy consumption before and after just for entertainment.
Put an hour meter on it and compare electric bills vs. hours.
I'll bet there's not enough difference to cover the cost of the high dollar insulation.

I would save the money and go with block mix if I were to add more insulation.

You could sculpt it into a space ship in memory of "the probe".

Michael Mortara
09-06-2012, 02:32 PM
Micropourous is tricky stuff, it can not get wet at all, it crumbles, it doesn't like to be handled, and it is the most expensive insulation out there.
That said, it has reduced my insulation profile to 5" and we can leave our hands on the furnace wall.
We talked about this at length on another thread, but combinations of different insulation types are often better than a single insulation profile.
If you have a 40# wire melter, keep it simple, larger furnaces will start to see real benefits with the more esoteric solutions.
Metal on the outside of a furnace will always be hot, tile board or such works best.
Want to save some money, turn down your furnace and figure out how to gather colder. Turning your furnace down fifty degrees from the top end of your working temp makes a big difference.