Loose-fill insulation can fill attic floors, wall cavities, and other hard-to-reach spaces where batts may not fit well. The main types are cellulose, fiberglass, and mineral wool; older homes may also contain vermiculite or perlite insulation that needs special care. Each material differs in thermal performance, fire behavior, moisture response, installation, and cost. Knowing those differences helps homeowners compare products and plan a project that meets local building requirements.
What Is Loose-Fill Insulation?
Loose-fill insulation consists of small particles or fibers that are poured or blown into a space. Contractors typically use a blowing machine to distribute the material across an attic floor or through holes drilled in a wall. It is also called blown-in insulation, although some loose materials can be poured into open cavities without a machine.
Unlike rigid boards or pre-cut batts, loose-fill material can conform around framing, wiring, pipes, and irregular surfaces. That flexibility makes it useful for retrofits and attic upgrades. Performance depends on more than the material: the installed depth, coverage, density, air leakage, and workmanship all matter.
Insulation slows heat flow, but it does not necessarily stop air movement. Sealing gaps around plumbing, wiring, chimneys, and other penetrations is often an important part of an insulation project. The U.S. Department of Energy recommends addressing air leaks and moisture problems before adding insulation.
Main Types Of Loose-Fill Insulation
Cellulose Insulation
Cellulose is usually made from recycled paper products, such as newsprint, that are treated with fire-retardant chemicals. It is available as loose-fill insulation for attics and as dense-pack material for enclosed wall cavities. Installers use blowing equipment to distribute it, and dense packing can help limit settling and air movement through a wall cavity when installed to the specified density.
Cellulose is valued for its high recycled content and ability to fill around obstructions. It is commonly used in existing homes because it can be installed through small access openings. Its R-value per inch varies by product and installation conditions, so homeowners should consult the product label and manufacturer’s instructions rather than assume one universal figure.
Cellulose can absorb and release moisture, but it should not be treated as a solution to roof leaks, plumbing leaks, or chronic dampness. Wet insulation may lose effectiveness and can contribute to building damage. Before installation, the attic or wall assembly should be checked for water entry and adequate ventilation where the design calls for it.
Fiberglass Insulation
Loose-fill fiberglass is made from fine glass fibers and is commonly blown into attics. Some products are also designed for wall cavities. Fiberglass is lightweight, does not provide food for mold, and is available from multiple manufacturers. Its thermal performance varies by product and installed depth.
Fiberglass does not prevent air leakage on its own. Wind washing—air moving through or across insulation—can reduce performance, particularly at exposed attic edges or in poorly detailed assemblies. Air sealing and proper installation around eaves, vents, and other features help the insulation perform as intended.
During installation, airborne fibers can irritate the skin, eyes, and respiratory tract. Installers should follow the product safety information and use appropriate protective equipment. Homeowners should avoid disturbing loose insulation unnecessarily and keep it clear of recessed lights or other heat-producing equipment unless those fixtures are rated and detailed for insulation contact.
Mineral Wool Insulation
Loose-fill mineral wool, also called rock wool or stone wool, is made from mineral materials spun into fibers. It is less common in residential loose-fill applications than fiberglass or cellulose, but certain products are designed for blowing into specific spaces. Product availability and permitted uses vary.
Mineral wool is known for its resistance to high temperatures and its ability to help control sound. It is also generally water-repellent, though that does not make an insulated assembly waterproof or eliminate the need to manage bulk water and moisture. As with other loose-fill materials, installers need to follow the product’s instructions for the cavity, density, and equipment being used.
Because loose-fill mineral wool is not offered in every market or for every application, homeowners should verify that a particular product is approved for the intended use. A product intended for open attic coverage may not be suitable for a closed wall cavity.
Vermiculite Insulation
Vermiculite is a lightweight, expanded mineral that was used as loose-fill attic insulation, including in homes built or remodeled during much of the 20th century. Some vermiculite insulation sold in the United States was contaminated with asbestos. The U.S. Environmental Protection Agency advises homeowners to assume that older vermiculite insulation may contain asbestos and to avoid disturbing it.
Vermiculite can be gray-brown or gold-colored and may have a pebble-like appearance, but appearance alone cannot confirm whether asbestos is present. If it is found in an attic or wall, it should not be swept, vacuumed, sampled, or moved by an untrained person. An asbestos professional can advise on testing and management. In many situations, leaving undisturbed material in place is safer than attempting removal.
Perlite Insulation
Perlite is a naturally occurring volcanic glass that expands when heated. Expanded perlite has been used in some loose-fill applications, including masonry cavities and specialized building assemblies. It is not as common as cellulose or fiberglass for typical residential attic insulation.
Perlite products should be evaluated according to their labeled application and local building requirements. Loose-fill material in an older building can be difficult to identify visually, so homeowners should not assume that an unfamiliar insulation is perlite or that it is harmless. When material may contain asbestos or another hazardous substance, professional assessment is the safer approach.
Comparing Loose-Fill Insulation Types
| Material | Common Residential Uses | Key Considerations |
|---|---|---|
| Cellulose | Attics; dense-pack wall retrofits | Recycled-paper content; fills irregular spaces; moisture sources must be corrected |
| Fiberglass | Attics; some wall cavities | Widely available; can irritate during handling; does not air-seal by itself |
| Mineral wool | Selected attic or cavity applications | Heat and sound performance; availability and approved uses vary by product |
| Vermiculite | Found in some older homes | May contain asbestos; do not disturb without professional guidance |
| Perlite | Specialized cavities and assemblies | Less common in residential retrofits; verify material and intended use |
R-value measures resistance to heat flow: a higher value means greater resistance, all else being equal. R-value per inch is not the only useful comparison. A deeper layer can provide more total thermal resistance, while gaps, compression, uneven coverage, and air leaks can undermine the result. Product labels and local energy-code requirements provide the most relevant figures for a specific project.
Where Loose-Fill Insulation Is Used
Attics
Attic floors are one of the most common locations for loose-fill insulation. Blown material can cover a large area and fit around framing, although it must not block soffit vents or cover equipment that needs clearance. Baffles can help preserve airflow at eaves, and markers can make the insulation depth easier to check after installation.
Before adding insulation, installers typically look for roof leaks, signs of pests, unsafe wiring, and gaps where indoor air escapes into the attic. Recessed lights, chimneys, and flues need appropriate clearances and protective details. The required clearance depends on the equipment and applicable codes; insulation should not be placed against heat-producing components unless the assembly is rated for that condition.
Existing Walls
Dense-pack cellulose or a product specifically designed for wall applications may be blown into enclosed cavities through drilled holes. This can improve insulation in an existing home without removing all the interior or exterior wall finish. Installers need to identify the wall construction and locate wiring, plumbing, fire blocking, and other obstructions before drilling.
Not every wall is a good candidate. Moisture-damaged walls, walls with certain existing materials, or assemblies that require special drying details may need repair or professional evaluation first. The installation method also matters: the product must reach the intended density and fill the cavity consistently.
Floors And Other Cavities
Some loose-fill products can be installed in floors, ceilings, or other enclosed cavities when the manufacturer approves that use. Gravity, vibration, and the cavity’s orientation can cause material to settle or shift. For that reason, an attic insulation product should not automatically be assumed suitable for a wall or floor.
How To Choose The Right Type
A useful comparison starts with the location and condition of the space, not just the material name. Homeowners can use these questions when comparing estimates:
- What area is being insulated? Attics, walls, and floors may require different products and installation methods.
- What R-value is planned? The target depends on climate zone, existing insulation, building design, and local code.
- How will air leaks be addressed? Ask whether air sealing is included or quoted separately.
- How will depth and coverage be verified? For attics, ask for the target depth and whether depth markers or documentation will be provided.
- Is the product approved for this application? Check its label, technical data, and installation instructions.
- Are there moisture, wiring, ventilation, or hazardous-material concerns? Resolve these before work begins.
Price depends on the material, job size, access, regional labor rates, existing conditions, and whether air sealing or repairs are included. A low bid may not include these tasks or may specify a different installed R-value. Comparing written estimates with the same scope and target performance is more useful than comparing a single total price.
Installation, Safety, And Building Codes
Professional installers use blowing equipment to distribute material at a specified depth or density. In attics, the work should account for ventilation, electrical boxes, recessed lights, chimneys, and access openings. In enclosed walls, installers need to choose an appropriate drilling and filling method and restore the openings afterward.
Loose-fill insulation should not be installed over unresolved roof or plumbing leaks. The space should also be checked for signs of mold, pests, or damaged wiring. Some older homes may contain asbestos-containing materials; vermiculite insulation is a particular concern. The EPA recommends avoiding disturbance and consulting qualified professionals when asbestos may be present.
Local energy codes and building requirements vary by jurisdiction and project. The Department of Energy’s climate-zone guidance can help explain regional insulation targets, but a local building department or qualified contractor can confirm which requirements apply. Homeowners can also look for contractors who follow recognized installation standards and provide product information, scope details, and documentation of the completed work.
Common Questions About Loose-Fill Insulation
Is Loose-Fill Insulation Better Than Batts?
Neither format is always better. Loose-fill can fit irregular areas and around obstructions, while batts may be easier to inspect and handle in open, regularly spaced cavities. Overall performance depends on the material, the assembly, air sealing, installation quality, and whether the product suits the space.
Can New Insulation Be Added Over Old Insulation?
Sometimes, but the existing material and attic conditions should be inspected first. Wet, contaminated, pest-damaged, or hazardous material may require special handling. New insulation should not conceal unresolved leaks or unsafe conditions, and older vermiculite should not be disturbed without professional advice.
Does Blown-In Insulation Stop Drafts?
Not by itself. Loose-fill insulation slows heat transfer but is not a substitute for sealing air leaks. A project that combines appropriate insulation with careful air sealing is more likely to address both heat loss and drafts.
Reliable Sources For Homeowners
For guidance, consult the U.S. Department of Energy’s insulation resources, the ENERGY STAR Seal and Insulate guidance, and the EPA’s information on vermiculite insulation. Product labels and manufacturer installation instructions are essential for confirming a material’s tested performance and permitted uses.