Lift the hatch in many Denver attics, and you will see one of two things: a gray blanket of shredded paper or a fluffy layer of white, pink, or yellow fibers. Both are loose fill, also called blown-in insulation, and both can bring an attic up to today’s levels. They are not the same product, though. The choice changes how deep the layer must be, how much it weighs, how much it settles, and how well it slows air leaks.
Cellulose packs more R-value into each inch, about R-3.2 to R-3.8, and it slows air movement better because it is denser. Loose fiberglass runs about R-2.2 to R-2.9 per inch, so it needs a deeper layer, but it weighs less, sheds water, and barely settles. Either one beats batts in most attics, because loose fill flows around wires, framing, and odd shapes without the gaps that batts leave behind. Batts still make more sense in open walls, floors, and other spaces where loose fill cannot stay in place.
Cellulose vs Fiberglass Loose Fill: Which Is Better for Denver Attics?
Both products work well when they go in at the right depth. Cellulose is the better pick when the attic floor has many obstacles or air leaks are hard to reach, since its density fills small gaps and slows airflow. It also softens outside noise a little more. In an attic that bakes in July, the best attic insulation for hot attics is whichever product goes in deep and even.
Loose fiberglass is the better pick when the ceiling drywall is older or the attic has a history of roof leaks, since it is lighter and sheds water. The pros and cons of cellulose insulation also include borate treatment, which adds fire and pest resistance. Blown fiberglass insulation will not burn and stays fluffy for decades when it stays dry.
Loose Fill Cellulose and Fiberglass Compared Side by Side
The table compares the two products on the points that matter most in an attic. Depths for R-38 come from Washington State University’s attic inspection guide, and the R-60 depths follow from the same R-value per inch.
Factor
Cellulose
Loose fiberglass
R-value per inch
About R-3.2 to R-3.8
About R-2.2 to R-2.9
Depth for R-38
10 to 12 inches
14 to 17 inches
Depth for R-60
About 16 to 19 inches
About 21 to 27 inches
Settling
Up to about 20 percent
Very little
Weight on the ceiling
Heavier
Lighter
Air movement
Slows it better
Lets more through
Water
Absorbs it
Sheds it
Fire
Borate treated, can smolder
Will not burn
Settling is the detail most people miss. Cellulose bags list both a starting depth and a settled depth, and the settled number is the one that counts. An installer who blows only to the settled number leaves the attic short a few years later.
When Loose Fill Insulation Beats Batts in a Denver Home
Batts and loose fill can reach the same R-value on paper. The installed result often differs, because batts need clean, open, regular cavities to work well. Loose fill comes out ahead in three common situations.
1. Attics Full of Wires, Pipes, and Framing
Batts must be cut and split around every obstacle, and each cut leaves a gap. Loose fill flows around wires, pipes, and truss webs and settles into the corners. That is why Denver batt insulation works best in open, regular spaces.
2. Topping Up an Existing Denver Attic
Most attics already have some insulation. Loose fill blows right over the old layer without crushing it, and it closes the gaps between old batts. Working out how much insulation an attic needs starts with measuring the depth already there. When a high energy bill traces back to the attic, a top-up is often the fastest fix.
3. Closed Walls in Older Denver Homes
Dense-packed cellulose can be blown into closed wall cavities through small holes, which batts cannot do. That makes it a common choice for older homes with empty walls. For some walls, foam injection in Denver is the other option.
When Batts Still Make More Sense Than Loose Fill
Loose fill is not the right answer everywhere. It needs a flat surface or a closed cavity to stay in place.
Open Walls During Construction or a Remodel
Open stud walls have no cover to hold loose fill in place, so batts or spray foam go in instead. Batts are quick to fit between studs and easy for an inspector to check before the drywall goes up. Some installers also staple fabric netting over open studs and blow fiberglass behind it, which fills the cavity as tightly as loose fill does in an attic.
Floors Over Garages and Crawl Spaces
Loose fill would fall out of an open floor cavity from below. Batts held up with wire supports, or spray foam, work in these floors and stay in contact with the subfloor.
Getting the Most From Loose Fill in a Denver Attic
Air seal first. Loose fill does not stop air on its own, and air leaks carry heat and moisture past even a deep layer. Our team at Grizzly Insulation CO seals the attic floor before any fill goes in. Build insulation dams around the attic hatch so the fill stays put, and keep baffles at the eaves so the vents stay open.
Front Range wind can push air through soffit vents and blow light fiberglass back from the eaves, a problem called wind washing. Baffles in each rafter bay hold the fill in place and keep the vent channel open. Cellulose is heavier and resists wind washing better, but it still needs baffles at the edges.
Depth is the next decision. Denver’s current code calls for R-60 in new homes, and most existing attics benefit from R-49 to R-60. Past that point, the diminishing returns of very deep attic insulation make more depth hard to justify. Summer heat matters too, and upstairs rooms that stay hot in Denver are often the first to improve, along with shorter air conditioning cycles.
Watch for moisture. Cellulose that gets wet from a roof leak or a bathroom fan venting into the attic packs down and loses value, and wet attic insulation in Denver should be dried or replaced. Denver’s dry air helps, but spring storms and ice at the eaves can still soak the edges.
Our team measures the current depth, looks for leaks and rodent damage, and seals the gaps first. Then we install blown-in insulation in Denver to the target depth, blowing cellulose past its settled number so the attic stays at its rating. For attics with a mouse history, we offer borate-treated insulation for pest control, which deters rodents. Grizzly Insulation CO finishes most attics in a single day, and our team is Building Performance Institute certified and insured.
Conclusion
Cellulose gives more R-value per inch, slows air better, and resists fire and pests through its borate treatment. Loose fiberglass weighs less, sheds water, and barely settles, but it needs a deeper layer. Both beat batts in attics with obstacles and in top-up jobs, while batts still win in open walls and floors. Seal the attic first and aim for R-49 to R-60. Grizzly Insulation CO can measure your attic and recommend the loose fill that fits it.
It can irritate skin during installation, so installers wear protection. Once it sits undisturbed in the attic, it does not affect the living space. Cellulose is dusty during installation too, so both products call for a mask in the attic.
Yes. Blowing loose fill over old batts is common and fills the gaps between them. Remove the old batts first only if they are wet, moldy, or soiled by rodents.
Plan on about 16 to 19 inches of cellulose or 21 to 27 inches of loose fiberglass, depending on the product. Check the bag chart, since each brand lists its own depth.
Loose Fill Insulation: Cellulose vs Fiberglass & When It Beats Batts
Lift the hatch in many Denver attics, and you will see one of two things: a gray blanket of shredded paper or a fluffy layer of white, pink, or yellow fibers. Both are loose fill, also called blown-in insulation, and both can bring an attic up to today’s levels. They are not the same product, though. The choice changes how deep the layer must be, how much it weighs, how much it settles, and how well it slows air leaks.
Cellulose packs more R-value into each inch, about R-3.2 to R-3.8, and it slows air movement better because it is denser. Loose fiberglass runs about R-2.2 to R-2.9 per inch, so it needs a deeper layer, but it weighs less, sheds water, and barely settles. Either one beats batts in most attics, because loose fill flows around wires, framing, and odd shapes without the gaps that batts leave behind. Batts still make more sense in open walls, floors, and other spaces where loose fill cannot stay in place.
Cellulose vs Fiberglass Loose Fill: Which Is Better for Denver Attics?
Both products work well when they go in at the right depth. Cellulose is the better pick when the attic floor has many obstacles or air leaks are hard to reach, since its density fills small gaps and slows airflow. It also softens outside noise a little more. In an attic that bakes in July, the best attic insulation for hot attics is whichever product goes in deep and even.
Loose fiberglass is the better pick when the ceiling drywall is older or the attic has a history of roof leaks, since it is lighter and sheds water. The pros and cons of cellulose insulation also include borate treatment, which adds fire and pest resistance. Blown fiberglass insulation will not burn and stays fluffy for decades when it stays dry.
Loose Fill Cellulose and Fiberglass Compared Side by Side
The table compares the two products on the points that matter most in an attic. Depths for R-38 come from Washington State University’s attic inspection guide, and the R-60 depths follow from the same R-value per inch.
Settling is the detail most people miss. Cellulose bags list both a starting depth and a settled depth, and the settled number is the one that counts. An installer who blows only to the settled number leaves the attic short a few years later.
When Loose Fill Insulation Beats Batts in a Denver Home
Batts and loose fill can reach the same R-value on paper. The installed result often differs, because batts need clean, open, regular cavities to work well. Loose fill comes out ahead in three common situations.
1. Attics Full of Wires, Pipes, and Framing
Batts must be cut and split around every obstacle, and each cut leaves a gap. Loose fill flows around wires, pipes, and truss webs and settles into the corners. That is why Denver batt insulation works best in open, regular spaces.
2. Topping Up an Existing Denver Attic
Most attics already have some insulation. Loose fill blows right over the old layer without crushing it, and it closes the gaps between old batts. Working out how much insulation an attic needs starts with measuring the depth already there. When a high energy bill traces back to the attic, a top-up is often the fastest fix.
3. Closed Walls in Older Denver Homes
Dense-packed cellulose can be blown into closed wall cavities through small holes, which batts cannot do. That makes it a common choice for older homes with empty walls. For some walls, foam injection in Denver is the other option.
When Batts Still Make More Sense Than Loose Fill
Loose fill is not the right answer everywhere. It needs a flat surface or a closed cavity to stay in place.
Open Walls During Construction or a Remodel
Open stud walls have no cover to hold loose fill in place, so batts or spray foam go in instead. Batts are quick to fit between studs and easy for an inspector to check before the drywall goes up. Some installers also staple fabric netting over open studs and blow fiberglass behind it, which fills the cavity as tightly as loose fill does in an attic.
Floors Over Garages and Crawl Spaces
Loose fill would fall out of an open floor cavity from below. Batts held up with wire supports, or spray foam, work in these floors and stay in contact with the subfloor.
Getting the Most From Loose Fill in a Denver Attic
Air seal first. Loose fill does not stop air on its own, and air leaks carry heat and moisture past even a deep layer. Our team at Grizzly Insulation CO seals the attic floor before any fill goes in. Build insulation dams around the attic hatch so the fill stays put, and keep baffles at the eaves so the vents stay open.
Front Range wind can push air through soffit vents and blow light fiberglass back from the eaves, a problem called wind washing. Baffles in each rafter bay hold the fill in place and keep the vent channel open. Cellulose is heavier and resists wind washing better, but it still needs baffles at the edges.
Depth is the next decision. Denver’s current code calls for R-60 in new homes, and most existing attics benefit from R-49 to R-60. Past that point, the diminishing returns of very deep attic insulation make more depth hard to justify. Summer heat matters too, and upstairs rooms that stay hot in Denver are often the first to improve, along with shorter air conditioning cycles.
Watch for moisture. Cellulose that gets wet from a roof leak or a bathroom fan venting into the attic packs down and loses value, and wet attic insulation in Denver should be dried or replaced. Denver’s dry air helps, but spring storms and ice at the eaves can still soak the edges.
Our team measures the current depth, looks for leaks and rodent damage, and seals the gaps first. Then we install blown-in insulation in Denver to the target depth, blowing cellulose past its settled number so the attic stays at its rating. For attics with a mouse history, we offer borate-treated insulation for pest control, which deters rodents. Grizzly Insulation CO finishes most attics in a single day, and our team is Building Performance Institute certified and insured.
Conclusion
Cellulose gives more R-value per inch, slows air better, and resists fire and pests through its borate treatment. Loose fiberglass weighs less, sheds water, and barely settles, but it needs a deeper layer. Both beat batts in attics with obstacles and in top-up jobs, while batts still win in open walls and floors. Seal the attic first and aim for R-49 to R-60. Grizzly Insulation CO can measure your attic and recommend the loose fill that fits it.
Frequently Asked Questions
It can irritate skin during installation, so installers wear protection. Once it sits undisturbed in the attic, it does not affect the living space. Cellulose is dusty during installation too, so both products call for a mask in the attic.
Yes. Blowing loose fill over old batts is common and fills the gaps between them. Remove the old batts first only if they are wet, moldy, or soiled by rodents.
Cellulose is denser, so it softens outside noise a little more. The difference is modest, and air sealing helps with sound as much as either product.
Plan on about 16 to 19 inches of cellulose or 21 to 27 inches of loose fiberglass, depending on the product. Check the bag chart, since each brand lists its own depth.