Roxul Comfortbatt insulation review – better than fiberglass

ROXUL Comfortbatt InsulationProduct: Roxul Comfortbatt Residential Stone Wool Insulation
Were to Buy:
Home Depot
Roxul ComfortBatt R15 16″ (12 Bags)
Roxul ComfortBatt R23 16″ (12 Bags)
Specification: Batts 16″ ( R15, 12 of 3.5×15.25×47), (R23 8 of 5.5×15.25×47) , (R30, 4 of 7.25×15.25×47); 24″ ( R15, 8 of 3.5x23x47), (R23 5 of 5.5x23x47) , (R30, 4 of 7.25x23x47)
Pros: Little higher R value per inch than fiberglass, does not hold moisture, denser so it absorbs more sound.
Cons: Cost more than fiberglass
Rating: 9 out of 10


Roxul Comfortbatt Insulation Product Overview

Roxul Comfortbatt is a fiber batt product similar to fiberglass insulation batts with a few difference that make it a better product.  Roxul is a stone wool, also called mineral wool, insulation made from basalt rock and iron slag recycle from steel production.  Where as fiberglass is mostly silicon dioxide Roxul has a mix of silicon dioxide and other oxides. Also the manufacturing process differ some what giving Roxul a higher density and fiberglass.   The higher density in turn reduces airflow through the insulation which no doubt contributes to a higher R-value and make Roxul an excellent sound absorber.  In fact Roxul makes a variant that is specifically for sound dampening called Safe’n’Sound. It is also very easy to cut and shape for good fit. Due to it similarity to fiberglass insulation it can easily substituted for fiberglass.

Roxul Comfortbatt Specs

Comfortbatt  comes in three R-value (15, 23, 30) with respective thickness of (3.5, 5.5, 7.25) inches and two widths (15.25 and 23) inches.

R15 R23 R30
Thickness 3.5″ 5.5″ 7.25″
Batts size 16″ 15.25 x 47 15.25 x 47 15.25 x 47
Batts per pkg 16″ 12 8 6
Surface area 16″ 59.7 sqft 39.8 sqft 29.9 sqft
Batts size 24″ 23 x 47 23 x 47 23 x 47
Batts per pkg 24″ 8 5 4
Surface area 24″ 59.7 sqft 39.8 sqft 30.7 sqft


Roxul Comfortbatt Features

Roxul Comfortbat has the following features:

  • Fire Resistance – Roxul stone wool can withstand temperatures up to 2150F (1177C) which limits the spread of fire and does not emit toxic gases.
  • Sound Absorbent – the unique non-directional structure of Roxul is denser than fiberglass which reduce airflow and sound transmission.
  • Water repellent – Roxul is water repellent yet vapor permeable.  It’s R-value is not effected by moisture.  It resists rot, mildew, mold and bacterial growth.
  • Dimensionally stable – It’s characteristics do no change overtime.  Environmental changes such as temperature and humidity can cause minimum changes in size and R-value.

Why I bought Roxul Comfortbatt

Roxul Insulation in AtticI was looking to renovate the insulation in my attic.  Being that my house was built in 1873 it did not originally have insulation.  It seems that around 1945 the then owners decided to use news papers as insulations. The floor and end walls of the attic are covered in newspapers and magazines from 1944 and 1945 to insulate.  Later in the 1970s there was blown in fiberglass insulation added.  It was a bit inconsistently applied and the in the 1990s some squirrels got into the attic and dug tunnels through it.  Even at best it was not much more than R13 and I wanted to bring it up to R38 which is the recommend (see Energy Star ) for the Maryland area.

The attic has 2×4 joist so I was looking at adding either 2×6 or 2×8.  I also wanted to keep the attic as storage so I preferred the 2×6.  The problem with fiberglass batting is that 3.5 inch is R13 and the 5.5 is R19 which only gives me R32.  Roxul is R15 and R23 so that would give me the R38 I wanted.

The more I looked at Roxul the more I liked it, not only could I get the R-value I wanted but it had several other features I liked:

  • Roxul has denser batts that minimize air flow also known as convective looping. Convective looping can reduce R-value as it gets colder.
  • Roxul is less affected by humidity than fiberglass.
  • Roxul is easier to cut to size than fiberglass.  I noticed that my attic floor joist were not always 16 inches on center so there was a potential for a lot of custom fitting.  As it turns out the ability to easily trim and fit the insulation was extremely helpful in the install.
  • Not specifically a Roxul thing but batts perform better than blown in.  They have higher R-value per inch to start with and maintain more of there R-Value at low temperature than blown in.

BTW while I looked at spray foam insulation I did not pick it because 1. I could not do it myself and 2. due to my house being historic I did not want to risk a bad job causing me to need to do any demolition to remediate.  If I was building a house I might consider foam.


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