PU expanding foam is a quick and effective way to fill gaps and holes, improving insulation and preventing drafts, moisture and pests.

What you’ll need

Gap-filling PU foam, water mister, safety goggles, gloves, sharp knife, brush or vacuum.

1. Preparation

• Remove dust, debris and loose material from the hole.

• Lightly mist the inside of the gap with water to help the foam cure.

• Shake the can thoroughly and attach the applicator.

2. Application

• Hold the can upside down during use.

• Apply foam from the bottom upwards, filling only around 50% of the space to allow for expansion.

• For deep holes, apply in layers, misting between applications.

3. Curing & finishing

• Foam skins in 5–10 minutes and fully cures within several hours.

• Trim excess once cured using a sharp knife.

• Sand, plaster or paint as required. Protect outdoor applications from UV exposure.

Key tips

• Shake the can regularly during use.

• Use gentle pressure for better control.

• Support through-holes with card or wire mesh before filling.