Found some spare bits of it in the attic, was curious what it is. Fibre glass?picture of insulation material

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    Looks like fiberglass to me too, but could be mineral/rock wool. Either way, not asbestos.
    – aaron
    Commented Jul 12, 2018 at 11:40
  • Definitely rockwool.
    – J...
    Commented Jul 12, 2018 at 16:42
  • When it comes to fiberglass vs rock wool, you can tell the difference by feeling it. Fiberglass is reasonably soft, but rock wool is stiff and scratchy. You wouldn't be advised to sleep on either, but you might actually get to sleep on fiberglass, while rock wool would be poking you too much with straw-like needles of slag, so you'd never be able to relax.
    – Hot Licks
    Commented Jul 13, 2018 at 0:23
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    You wouldn't get to sleep the next day, though. Fiberglass is itchy, just with a delayed effect... ...... and all of them, the microfibers are also cancer vectors like asbestos, just not as aggressive or nearly as famous. If you work with any of them occupationally, use PPE. Commented Jul 13, 2018 at 17:16

5 Answers 5


No, that is fiberglass. When it comes to asbestos insulation, it is found only in loose fill types, and in a solid board configuration. Asbestos was never used in a batt form of insulation which is what your picture is of.


  • 6
    it's still not something you want to work with without protective gear. Commented Jul 12, 2018 at 11:43
  • 3
    Absolutely - gloves, glasses, mask, and wear long sleeves and legs and ideally tape the ends to your gloves and socks. If you're working with it - but the question asked was about what it was, not how to work with it :) Commented Jul 12, 2018 at 11:47
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    – Kris
    Commented Jul 12, 2018 at 12:24

Asbestos did come in a board configuration for use in furnaces and combustion chambers. But that is not asbestos. It is probably Kaowool or a similar product

  • 1
    Johns Manville makes a mineral wool insulation that also looks similar
    – Machavity
    Commented Jul 12, 2018 at 15:06
  • 2
    The picture is of batt insulation not board :) Commented Jul 12, 2018 at 15:07
  • Not kaowool - 99% it's Roxul.
    – J...
    Commented Jul 12, 2018 at 20:42

The typically greenish colour and the smaller gaps between the fibres suggest to me that it's mineral wool (aka "rockwool", although that's technically a brand name) rather than fibreglass. The two have pretty similar properties, but mineral wool is generally slightly more irritating to handle ... I'll handle fibreglass without gloves if I have to, but I won't go near mineral wool without good protective equipment because I'll be itching for days if I do.


Either fiberglass or rockwool. Take a small piece outside and apply flame to it. Fiberglass will melt, rockwood won't.

  • That must be a hot flame. Common fiberglass melts at 1700 F. Butane torches are 1400~. Commented Jul 13, 2018 at 16:11

Dang, that's tough. I want to say it's mineral wool but the sides are more puffed out than they should be from the factory, but that happens as soon as it rubs against something. 99.99% sure it's mineral wool. I've worked with that stuff for two house builds. The part that tells me it's mineral wool is the stamp pattern on the face (left side in photo). That's the same stamp that is used once it's super heated (* not actual term) and compressed into a batt. It's excellent (and itchy) stuff. I don't care who you are, it's not "fun" to work with as they market it. Cut into it, and try installing it in the house without a mask. Guaranteed problems that evening and you will hack up black crap. It's very good stuff, just wear proper gear. I learned the first time around and invested in a suit and proper mask.

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