I have excess cellulose / blown-in insulation. Can I compost that in my backyard, as it is essentially wood? I do not plan on using it for composting with plants that produce vegetables or fruit.

While I could repurpose it, I prefer working with rigid foam, fiberglass, on the expanding foam.

The cellulose is at least 15 years old. Would it have been common place for it to be treated with chemicals then render it unsafe for composting?

  • 1
    I never thought of this: If it is biodegradable, wouldn't using this stuff just make the attic into a huge compost bin? Wouldn't all homes that use it have to replenish after a certain period?
    – gns100
    Commented Jun 11 at 15:17
  • 6
    @gns100: The house is made of wood. Biodegradable does not mean it degrades under normal use when properly protected -- in specific, when dry and not in contact with soil organisms.
    – keshlam
    Commented Jun 11 at 15:19
  • Websearch for "brominated biodegradable" turns up several scientific studies of this question.
    – keshlam
    Commented Jun 11 at 15:20
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    For what it's worth, "biodegradable" and "suitable for composting in my yard" are two very different things. The title was a bit misleading as many things are biodegradable while being severe health hazards. I've revised it.
    – isherwood
    Commented Jun 12 at 16:05

3 Answers 3


Maybe! Sorry it's not a more definite answer.

While you can compost it, it will be treated with a fire retardant of some sort. That might be borax, boric acid, and/or ammonium sulfate, all of which are relatively OK to have out in the environment.

What is more worrisome is the fact that it might be made from recycled newsprint or other printed materials. The inks used could have all sorts of chemicals in them such as heavy metals. Putting those out in the environment isn't the best idea.

As a result the best practical uses are reuse if it's still in good condition, or sanitary landfill if it is not.

Way more details are available at this NIH study if you happen to have insomnia.


Cellulose is treated for fire resistance (and possibly against mold). It'll break down for sure, but it'll leave chemicals behind. I'd put it on your local marketplace for cheap and recover some value.


The "acid test" is probably to try incinerating a small amount of it. If it burns easily, it should decompose under the right conditions.

If not, then you know it has been heavily treated, and should either go to landfill or to a high-temp incinerator if possible.

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