Glasswool vs Polyester Insulation: Which Ceiling Insulation is Best for NZ Homes?

Choosing the right ceiling insulation is one of the most important decisions you can make to improve your home’s energy efficiency, comfort, and long-term performance.

In New Zealand, two of the most popular insulation types for ceilings are glasswool and polyester. Both have distinct advantages and considerations depending on your goals, budget, and property type.

In this guide, we’ll break down the key differences between glasswool and polyester insulation, including:

By the end, you’ll have a clear understanding of which insulation option may suit your home best.

What is Glasswool Insulation?

Glasswool insulation (also called fibreglass insulation) is made from recycled glass and sand, spun into fine fibres to create a soft, wool-like texture.

It has been widely used in New Zealand for decades, with common brands including Pink Batts, Earthwool, and Bradford Gold.

Key Benefits of Glasswool

• Excellent thermal performance
• Affordable and widely available
• Lightweight and easy to cut to size
• Often has high fire resistance
• Good acoustic insulation properties

What is Polyester Insulation?

Polyester insulation is made from synthetic polyester fibres—similar to those found in pillows and duvets.

It’s popular with homeowners looking for a non-irritant, hypoallergenic insulation material. Common brands in New Zealand include Mammoth and GreenStuf.

Key Benefits of Polyester Insulation:

• Non-irritant, safe to handle without protective gear
• Hypoallergenic—ideal for those with sensitivities
• No slumping or settling over time
• Often made from recycled plastic (PET bottles)
• Low moisture absorption

Glasswool vs Polyester: Performance Comparison

Thermal Performance (R-Value)

Both glasswool and polyester insulation are available in a range of R-values (which measure thermal resistance).
Generally speaking, both materials can achieve similar R-values per thickness.

• Glasswool: Slightly higher R-values per cm of thickness in many cases.
• Polyester: Slightly thicker to achieve the same R-value.

Verdict: Comparable thermal performance, but glasswool may take up less space for higher R-values.

Cost Comparison (Installed Price in NZ)

Here’s an approximate price range for ceiling insulation per m² in New Zealand (installation included):

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Glasswool generally remains the cheaper option, both in terms of material cost and installation.

Verdict: Glasswool is more budget-friendly; polyester is premium-priced.

Health & Safety

This is where the biggest difference lies:

• Glasswool: Can cause skin irritation, itchiness, and respiratory discomfort if handled without proper protection.
• Polyester: Non-toxic, non-irritant, safe to install without gloves or masks.

Verdict: Polyester wins for health and ease of handling, making it popular for DIY installs and sensitive households.

Environmental Impact

• Glasswool: Often contains recycled glass (up to 80%) and uses natural raw materials, but production can be energy-intensive.
• Polyester: Commonly made from recycled plastic bottles (PET) and is fully recyclable at the end of life. However, it’s still a synthetic product derived from petroleum.

Verdict: Both have recycled content, but polyester often edges out in recyclability and circular economy credentials.

Installation Process

• Glasswool: Easy for professionals to install but requires protective gear. Can compress over time if installed poorly.
• Polyester: Easy to install, holds its shape well, and doesn’t sag or settle over time.

👉 Verdict: Polyester is easier for DIY installs; both perform well if installed correctly by professionals.

Which Insulation Type is Best for You?

Choose Glasswool if:

• You want the most cost-effective insulation solution
• You’re comfortable hiring professionals for installation
• Maximising R-value per cm is essential (for tight spaces)
• You want proven, widely available products

Choose Polyester if:

• You value non-toxic, hypoallergenic materials
• You’re doing a DIY install or concerned about handling
• You want insulation that will retain its shape and performance over decades
• You’re happy to invest a bit more upfront for peace of mind

Why Ceiling Insulation Matters in NZ

In New Zealand’s climate, ceiling insulation is one of the most important ways to:

• Prevent up to 50% of heat loss during winter
• Improve home energy efficiency year-round
• Meet Healthy Homes Standards for rental properties
• Boost home comfort, making spaces warmer in winter and cooler in summer

Try Our Insulation Cost Calculator (NZ’s Most Accurate!)

Still unsure about insulation costs for your property?
We offer New Zealand’s most accurate insulation cost calculator, designed specifically for Kiwi homes.

Quickly estimate the price of:

• Glasswool Ceiling Insulation
• Polyester Ceiling Insulation
• Moisture Barriers
• Insulation Removal & More

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