Attic Insulation

What type of insulation is this? House built in 1919. Insulation is white, light and fluffy. No, I did not taste it.


It’s hard to tell from photos, but resembles Perlite. Even though it’s not designed as loose fill attic insulation I’ve seen it used in this matter before.

Very difficult to tell from the pic’s, but by your description, I would say possibly rock wool.

Good info thanks … Roy




That description of rockwool from E-how is way off base…strike it from your database!!!

Certainteed (and probably a few others) produced a pure white, long fiber blown fiberglass insulation in the 1980-90’s that became known as the “fluffer’s delight”…by using more air in the settings on the equipment, the installer could fluff the long fibers and get lots of depth with less material- less material meant less R factor but to the untrained eye, 13.5" depth should be an R40, but could be 25-40% less actual R!!!

In these cheating installations, due to convection in the upper portions of the loose open fibers, R-value actually dropped as the outdoor/attic temps dropped (proved by experiments at Oak Ridge National Labs). A solution to reduce the convection/heat loss at the upper layer was to blow at least 2-3" of cellulose to create a “cap” for the insulation blanket.

This home is 93 years old .



If you bothered to read the entire, very short description, it briefly touches on what you are saying…

And as Roy mentioned, this home is almost 100 years old. I guarantee you that is not “modern day” insulation in that attic!


Did you feel the insulation for texture?
If it was firm/hard/rock like, it is probably perlite.
If it was soft, almost cloth like, it is most likely rock wool.

What is Rock Wool insulation?

Gotcha the first time Joe. :wink:

Care to add to the discussion, and tell us why you call it as Perlite, when the pic’s are inconclusive? With out more info from Buck, it is anyone’s guess.

My comments on the E-how article:

<LI class=step itxtHarvested=“0” itxtNodeId=“7”>*1 *“Examine the texture of the insulation and look for the appearance of tiny white balls of fabric. Rock wool insulation looks very much like large masses of cotton balls.”

After being in and around the energy conservation field since 1977, I am saying that I have never seen any rockwool insulation that would fit that description!!

<LI class=step itxtHarvested=“0” itxtNodeId=“6”>*2 *"Look at the color of the insulation to determine if it is rock wool. Insulation that is pure white is almost always rock wool. However, rock wool can also be tan or gray as well and sometimes has black spots on it."

Again from my experience, I have never seen pure white rock wool insulation; only fiberglass, a Canadian product from ground-up, re-cycled drywall factory rejects/seconds and perlite are white or pure white.

<LI class=step itxtHarvested=“0” itxtNodeId=“5”>3 “Examine the density of the balls of fiber. Rock wool is applied wet and therefore settles under the weight of the moisture. For this reason, the insulation is very tightly packed together with very few air holes. It is not light and fluffy on top.”

Rock wool was never loose blown as a wet product into residential attics. In some cases in the past, it was spray applied with adhesives to give fire protection to steel beams and other surfaces as required by codes in commercial, industrial, etc…but that is not this attic with a loose, probably hand-poured, expanded perlite with another product underneath it.

<LI class=step itxtHarvested=“0” itxtNodeId=“4”>4 “Look in the attics and walls of homes built prior to the mid 1990s. In the mid '90s, rock wool began to be replaced by more modern fiberglass insulation. Although rock wool is still manufactured, most of it exists in older homes and manufactured homes.”

BTW, I was not saying that the product in question was fiberglass but just adding some extra info about the some of the PURE WHITE fiber insulations that were being cheated with in the 1980-90’s.

Also, perlite enjoyed a bit of a boom in the early-mid 1980’s, after a short article was published in “Popular Science” magazine. Just because the house is old does not mean that all insulation in it is old also. I have installed insulation in uninsulated 130-150 year old homes in the past 2-3 years.

Keep one very important fact in mind… you are in Canada, and Buck (and I) are in the U.S.
Many of your ‘points’ do not apply here. I see “pure white” (except for dust) rock wool very often.
Yes, about old houses with new insulation. In fact, many homes 100+ years old around here had NO insulation when built. Many still don’t, especially in the walls. K&T was BIG around here!
PS… don’t be so literal with the “cotton balls” comment. It is a simplified description for a DIY’er, not HI’s.

Until Buck provides more information, we have no idea what it is. Only speculation.

pic is perlite

do you think something different?

The material was soft & light.