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EPS vs XPS vs EPS with graphite

rambodim | Posted in General Questions on

Hi all,

First of all, thanks for your time reading this.

I would like an advice from you about thermal insulation of the outer walls of my house. My biggest problem is that path that I walk to get inside my home passes between my home and neighbors’ house. This path is wide 110cm. So as you can guess every cm counts 🙂 and I need to find best insulation with smaller with and best price 🙂

My questions are:

1. Is it true that isolating your house with example 3 cm XPS gives you results like isolating your house with ~6 cm EPS? Is it true that XPS creates moisture and fungi because it doesn`t let the wall то “breathe” ?
2. Is it true that EPS with graphite gives you 20% better results then regular EPS? Can I say that 5 cm EPS with graphite replaces 6 cm EPS?
3. Can EPS with with of 5 cm be enough to “feel” the benefits of isolating the house?

Climate in my country varies from -10°C [14°F] in winter to 40°C [104°F] in summer. I am planning to heat on wood and inverter air conditioner.

I hope that I express my self good, since English in not my native 🙂

Thanks again, if you have any question please write.

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  1. GBA Editor
    Martin Holladay | | #1

    You have listed three types of insulation:

    1. EPS (expanded polystyrene). The R-value (insulating value) of this insulation varies with density. Typical R-values for EPS range from R-3.1 to R-4.2 per inch -- a wide range. Check with local distributors to see what types are available in your country.

    2. EPS with graphite. The best known brand of this type of insulation is BASF Neopor. The R-value of Neopor varies from R-4.4 to R-4.7 per inch -- so it is true that it has a better insulating value than ordinary EPS.

    3. XPS (extruded polystyrene). The R-value of XPS is R-5 per inch in North America, but about R-4 per inch in Europe (because European manufacturers use a different blowing agent from North American manufacturers). Check to see what types of XPS are available in your country, and research the insulating value of these products.

    If you live in a cold climate, thin insulating foam on the exterior side of your walls may trap moisture. In warmer climates, there is no concern about trapping moisture when installing exterior foam. For more information on the minimum required R-values to prevent moisture problems when installing exterior foam, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

    Your climate, where the winter temperature never gets colder than -10°C, sounds similar to U.S. Climate Zone 3. We would consider that a warm climate. I don't think that you have to worry about trapping moisture in your walls in your climate, no matter what type of insulation you choose, or how thick it is. (Of course, thicker insulation always performs better than thin insulation.)

    If you tell us what country you live in -- from your name, I'm guessing Macedonia? -- we can give you more specific advice.

  2. Reid Baldwin | | #2


    What is the rest of the wall (concrete block, wood frame with cavity insulation)? How thick?

  3. rambodim | | #3

    Thank you for your time and attention Martin and Reid.

    The structure of external wall is a 2-3 cm (~1 inch) layer of concrete (plaster), then a hollow brick around 25-30 cm, then again 2-3 cm layer of concrete (plaster). It was build 25 years ago.
    Yes, I live in R. of Macedonia, excellent guess :), climate in winter is usually not bellow -10 C but sometimes it can get bellow that for a week for example.

    There are available ESP foams with different kg/m3, from 13-30 but this vary depending the thickness of foam (some example in the link below)

    As I understand in your answer, price of XPS (60% more in my country) does not justify the R-value because they are ~ same R-4 as the ESP with graphite. Or am I wrong :)

    So, is for example, 5 cm ESP with graphite the minimum for insulating the house?

  4. GBA Editor
    Martin Holladay | | #4

    Yes, I would guess that you should choose EPS with graphite, not XPS, especially if XPS costs 60% more.

    Since your walls are of masonry construction, there are no possible worries about trapping moisture. Moisture won't hurt your walls. The exterior foam will help keep your walls dry.

    There is no minimum amount of insulation for performance purposes. In general, the more, the better -- until the insulation gets so thick that it costs more to install than it will ever save on your energy bills. There may be regulations in your country that govern minimum insulation levels -- if so, you should inquire locally to find out what your local laws require.

    Here in North America, most experts would advise that an appropriate level of insulation for the wall you describe, in your climate zone, would be about R-10 or R-15. That means 6 cm. to 8 cm. of rigid foam. If you have to install less because your walkway is narrow, that is something to consider.

  5. rambodim | | #5

    Thank you again for simplifying things for me. You saved me a lot of nerves :)

    All the best

  6. charlie_sullivan | | #6

    I would guess that ordinary EPS is the best as far as insulating value for a given amount of money, but the graphite version gives you more insulating value in a limited amount of space.

    Note that the R-values that Martin is describing are based on the US units--to get the SI units used in Europe, multiply by 0.176, so his recommendation of R-10 to R-15 becomes R-1.75 to R-2.65, or in round numbers R-2 to R-2.5.

  7. Expert Member
    Dana Dorsett | | #7

    The weather in Macedonia is more akin to US climate zone 4A much cooler than US climate zone 3. The hourly-averaged temperature for the month of January in Skopje runs about 0C/+32F, which is comparable to say, Newark, New Jersey. The annual base 18C heating degree days are 2646 (source: ), which is ~4675 HDD base 65F, which is comparable to Newark's ~4812 HDD ( )

    From a comfort point of view even 2"/ 5cm of EPS (any type) on the exterior side of a concrete block (or hollow clay brick) + plaster is pretty good, and would meet building requirements in the US climate zone 4A, due to the benefit of having the "thermal mass" of the wall inside the insulation. If your heating fuel is expensive it can still be rational to go as deep as 3" / 7.5cm, but not as deep as 10cm. With 10cm of EPS on the exterior of a masonry wall it would meet the requirements for US climates comparable to the climate Sweden. But energy costs in the US may be considerably lower than in Macedonia. With higher energy costs thicker the insulation can still make economic sense.

    Still, the money you spend for anything more than 5-6cm might be better to use for other things. For instance, if your windows are a single thickness of glass rather than 2 layers separated by 5-15mm, improving the windows will be more important to comfort and energy use than going from 5-6cm of EPS to 8-10cm.

    So, how do you heat this house, and how much does the fuel cost?

  8. GBA Editor
    Martin Holladay | | #8

    In his original question, he said he is heating with firewood.

    Since I recommended the use of 6 cm. to 8 cm. of rigid foam, it sounds like our recommendations are in the same ballpark. Thanks for digging into the climate zone issue a little further than I did.

  9. Expert Member
    Dana Dorsett | | #9

    Oops! Missed that!

    Firewood varies a lot in price regionally, but I'll assume that it's likely to be fairly low cost and widely available, in which case 5-6cm of foam still makes sense, but probably not much more.

    The cost difference between an inverter heat pump rather than an air-conditioning-only is not very much, and is probably going to be worth it. That depends a lot on what electricity costs, and how reliable it is. Average electricity prices in Macedonia are comparatively cheap at about 8-9 Euro cents per kwh:,_second_half_2014_%28%C2%B9%29_%28EUR_per_kWh%29_YB15.png

    It may be cheaper to heat with a heat pump during milder weather than with wood, unless you cut & split your own wood from cheap or free resources, or are burning scrap lumber.

  10. rambodim | | #10

    Thanks again everybody for your time reading and finding solutions about my problems :)

    Luckily I have windows 2 layers separated by 5-15mm :) so I expect them not to be weak link in the chain :)

    Yes it is true that we do have a bit cheaper kw BUT our average salary is 350 euros :(. Wood is around 50 euros per m3. That why I thought to have both of them in combination since in colder days to use wood as primary heat provider and inverter to help because inverter is not that good in -10 degrees and it efficiency drops.

    I would like to consult about one more thing. Since EPS with graphite comes with density of 15kg/m3 on 5cm but higher R value, how it will compare with regular EPS with 3cm but 30kg/m3? It will be better, similar?

    Thanks again, you have been so nice.

  11. GBA Editor
    Martin Holladay | | #11

    You need to ask the manufacturer of the EPS (or the distributor or seller of the EPS) about the material's R-value (insulating value). In the U.S., this information can usually be found by visiting the manufacturer's web site.

  12. Expert Member
    Dana Dorsett | | #12

    Type-I EPS is about 16kg/m^3, and fairly soft, easy to break. Graphite loaded Type-I EPS is the 15kg/m^3, will probably outperform Type-II EPS or even Type-IX EPS, but not by a lot.

    Type-II EPS is about 24kg/m^3, Type-IX EPS is about 32kg/m^3, so the 30kg/m^3 EPS will perform similar to Type-IX EPS from any US vendor. Type-IX EPS is much more rigid than Type-I EPS, and harder to damage.

    At about R4.5/inch when the average temp through the foam is about 24C (75F) the R-value (US units)of Type IX is about R4.3 @ 2.5 cm thickness.

    When the average temp through the foam is +4.5C (40F) it's performance rises to about R4.75 @ 2.5cm. That is the performance to expect when it's about 20C indoors, and -10C outdoors.

    That is not dramatically lower than graphite-loaded Type II (24kg/m^3) graphite loaded NeoPor EPS, and Type-I graphite loaded EPS will perform slightly lower than the lowest of these numbers:


    Compare that to standard EPS at different densities:

    Given that the lower density foam is more fragile and the higher density foam is easier to work with, going with 30kg/m^3 standard foam that is 1cm thicker than graphite loaded 15kg/m^3 foam is a better value. It will be easier to install, and will deliver higher performance. If it normally comes in 3cm thick sheets, use two layers.

    If you use only 1 layer at 5cm the graphite loaded low density foam will perform at about R9.5 when it's -10C outside. That would meet US requirements in a similar climate. With 3cm of standard higher density EPS will perform at about R5.7 at -10C outside, which would not meet US requirements in that type of climate. But with two layers (6cm) of the standard high-density foam it will perform at about R11.4. about 50% more than would be required in the US. At 6cm it may be more expensive than 5cm of graphite loaded foam, but even if that is true it may still be worth it as a long term investment. It's almost certainly true that 5cm of foam (any type) would a better long-term investment than only 3 cm of foam.

  13. rambodim | | #13

    Thank you Dana, thank you all. You all know how to present things in simple way to a noob when it comes for insulation :)

  14. rambodim | | #14

    Sorry to dig this thread again, but when I went to the warehouse for insulating materials, seller told me about rock mineral wool. Specifically this one

    Is EPS with graphite still better insulating material then rock mineral wool?

    I plan to use 5 cm.
    Thanks again.

  15. GBA Editor
    Martin Holladay | | #15

    Once again, you should know that the best way to determine the R-value (insulating value) of materials that you purchase in Macedonia is to ask the distributor or the manufacturer what the R-value is.

    Here in the U.S., EPS with graphite usually has an R-value of R-4.4 to R-4.7 per inch. Dense panels of mineral wool insulation usually have an R-value of R-4.0 or R-4.1 per inch, although some mineral wool products have lower R-values.

    In other words, the R-value of mineral wool is less than that of EPS with graphite -- but the difference between the products is not very great.

  16. rambodim | | #16

    Thanks Martin.

    Thing is, here if I go to the distributor and ask what is R value of this material I will get face like o.O :D :). Salesman say that everything is best for you no matter what you ask :).
    Technical data is almost impossible to find, so only option is to ask the manufactures in my country. My guess is that, they will think that either I am an spy from competition or God know`s what :)

    Thanks again everybody, for your patience and advice.

  17. Dana1 | | #17

    The Knauf rock wool data sheet does specify it's thermal conductivity as λD= 0.036 W/mK, which is fairly typical for low density rock wool batts.

    That would be the amount of heat in watts that passes through at one square meter of wall area if the insulation has a thickness of 1 meter, when the temperature difference is 1º C (or 1º Kelvin).

    So at 3 cm it would be 0.036 W/mK x 1m/0.03m= 1.2 W/ºK. It's RSIvalue is then 1/1.2= RSI 0.0833

    That becomes R4.73 when converted to US units. At (30mm/25.4mm per inch=) 1.2" that is a ratio of about R3.94 per inch of thickness. That would typical for low density rock wool, but a bit low for high-density rigid rock wool. It is comparable to low density Type-I EPS without graphite, and lower performance than EPS with graphite.

    Most rock wool sold in the US has a λD= 0.033 W/mK to 0.034 W/mK, (or about R4.2- to R4.3 per inch.)

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