Insulating bathroom walls requires materials that can withstand high humidity and prevent mould growth. Selecting the right insulation ensures energy efficiency, comfort, and durability. Here’s a guide to the best insulation options for bathroom walls:

1. Extruded Polystyrene (XPS) Foam Boards

XPS foam boards are rigid panels known for their excellent moisture resistance and thermal performance. They are ideal for bathroom walls due to their ability to repel water and prevent mould formation. 

Advantages:

  • High R-value per inch, providing effective insulation.
  • Resistant to water absorption, reducing the risk of mould.
  • Durable and long-lasting.

Considerations:

  • Must be properly sealed at joints to maintain moisture resistance.
  • Slightly more expensive than other insulation types.

2. Closed-Cell Spray Foam Insulation

Closed-cell spray foam expands upon application, creating an airtight and moisture-resistant barrier. It’s particularly effective in bathrooms where space is limited and moisture control is critical.

Advantages:

  • Excellent air sealing properties, reducing drafts.
  • High R-alue, enhancing energy efficiency.
  • Acts as a vapour barrier, preventing moisture infiltration.

Considerations:

  • Requires professional installation.
  • Higher upfront cost compared to other insulation types.

3. Rigid Foam Insulation (EPS)

Expanded Polystyrene (EPS) foam sheets are lightweight and easy to install. They offer good moisture resistance, making them suitable for bathroom applications. 

Advantages:

  • Cost-effective and readily available.
  • Resistant to moisture and mould.
  • Easy to cut and fit into wall cavities.

Considerations:

  • Lower R-value compared to XPS or spray foam.
  • Less durable over time in high-moisture environments.

4. Mineral Wool (Rockwool) Insulation

Mineral wool is made from volcanic rock and offers excellent fire resistance and soundproofing qualities. It’s also water-resistant, making it a viable option for bathroom walls.

Advantages:

  • Non-combustible, enhancing fire safety.
  • Excellent acoustic insulation, reducing noise transmission.
  • Resistant to moisture, mould, and mildew.

Considerations:

  • Heavier than other insulation types, requiring secure installation.
  • Can be more expensive than fiberglass or EPS.

5. Fiberglass Insulation with Vapour Barrier

Fiberglass batts are a common insulation material. When used in bathrooms, it’s essential to select fiberglass with a vapour barrier to prevent moisture accumulation.

Advantages:

  • Affordable and widely available.
  • Easy to install for DIY projects.
  • Provides good thermal insulation.

Considerations:

  • Must be properly sealed to prevent moisture ingress.
  • Can lose effectiveness if it becomes wet.

Additional Tips for Bathroom Insulation

  • Use Moisture-Resistant Plasterboard: Also known as green board, this drywall is designed for high-humidity areas and helps prevent mould growth.
  • Ensure Proper Ventilation: Installing an exhaust fan reduces humidity levels, protecting insulation and preventing mould.
  • Seal All Gaps: Use caulk or foam sealant around windows, doors, and plumbing penetrations to prevent moisture intrusion.

Selecting the appropriate insulation for bathroom walls is crucial for maintaining a comfortable and healthy environment. Consider factors like moisture resistance, thermal performance, and installation requirements when choosing the best option for your bathroom.