The Difference Between Fibreglass Batts Vs Blown Insulation for Insulating Walls

Choosing the right insulation makes a big difference to how warm and dry your home feels. Two of the most common types used in New Zealand are fibreglass batts and blown insulation. Many homeowners ask about the difference between fibreglass batts vs blown insulation. Both are designed to slow heat loss, but they are installed in different ways. For existing homes, especially when insulating walls, blown insulation is often the better option. 

Fibreglass Batts vs Blown Insulation 

What Are Fibreglass Batts 

Fibreglass batts, sometimes called blanket or segment insulation, are manufactured in rolls or pre-cut lengths. They are placed between timber framing, such as wall studs. The product is shaped to fit the cavity and is usually made from fibreglass, although other fibres are sometimes used. 

When installed carefully, they can perform well. The problem comes when they are not cut and fitted with precision. Any gaps or spaces between the batts and the framing reduce their effectiveness. If they are too short, not pushed firmly to the edges, or cut poorly around pipes and wires, warm air escapes through those gaps. Over time, fibreglass batts can also sag or shift, leaving cold spots and lowering their thermal performance. 

However, installing fibreglass batts into existing walls is very difficult. To do so, you must remove the wall linings, which is costly, messy, and disruptive. This makes batts an impractical option for most retrofit wall insulation projects. 

What Is Blown Insulation 

Blown insulation is a loose-fill product made from dry glasswool fibres. It is installed using specialised equipment that blows the insulation into the wall cavity. This process allows the insulation to spread evenly, filling every space including tight corners, gaps around pipes, and awkward areas around framing. 

Because the product flows freely, it forms a continuous layer with no joins or weak spots. It won’t slump, shrink, or leave gaps once in place. The result is a much more complete thermal seal, which makes a big difference to how well your home holds its warmth. 

Insulating Existing Walls 

One of the main advantages of blown insulation is that it can be retrofitted into existing walls without removing the internal linings. This is especially important for New Zealand homes built before the 1990s, which often have little or no wall insulation. 

Our process involves drilling small, tidy holes into either the internal wall lining or the external cladding. The insulation is blown into the cavity until it is full, then the holes are sealed and finished. The result is fully insulated walls with minimal disruption to your home. This is something fibreglass batts cannot achieve unless the wall linings are already removed. 

A Better Choice for retrofit Wall Insulation 

When comparing fibreglass batts vs blown insulation for existing walls, the difference is clear. Batts are not a practical option unless you are already renovating and have the linings off. For most retrofit projects, CosyWall blown insulation is the smarter choice. It fills the entire wall cavity, creating a complete thermal barrier without the need to remove gib or cladding. 

If your home has cold walls or was built before wall insulation standards, CosyWall can make a big difference. Our system is CodeMark certified, safe, and durable, giving you peace of mind that it will keep your home warmer, drier, and healthier for years to come. 

Try our wall insulation cost calculator or contact us today to book your free home assessment and let our team show you how CosyWall Insulation can help improve your home’s thermal performance.