Why Is My Pipe Insulation Sweating?

Why Is My Pipe Insulation Sweating?

Troubleshooting Condensation on Insulated Pipes

If your insulated pipes are sweating (condensation forming on the outer surface of the insulation), something is wrong. This guide explains the common causes and how to fix them.

What is "Sweating" Insulation?

Sweating occurs when moisture condenses on the outer surface of the insulation, causing water droplets on the insulation surface, damp or wet insulation, dripping water, and mould or mildew growth. Wet insulation loses thermal performance, causes water damage, and indicates system failure.

Common Causes & Solutions

1. Insulation Too Thin

Cause: Insulation thickness insufficient to keep outer surface above dew point.

Symptoms: Entire insulation surface is damp, worse in high-humidity conditions, condensation forms evenly across surface.

Solution: Increase insulation thickness — chilled water: upgrade from 13mm to 19mm or 25mm; refrigeration: upgrade from 19mm to 25mm or 32mm.

See thickness selection guide →

2. Unsealed Joints

Cause: Gaps at joints allow moisture to penetrate insulation and reach cold pipe surface.

Symptoms: Condensation at specific joints or seams, dripping from joint areas, insulation feels damp at joints.

Solution: Re-seal all joints with K-FLEX 800 adhesive, or replace with K-FLEX SK self-seal tubes. Ensure 25mm overlap at butt joints.

See joint sealing guide →

3. Wrong Material (Open-Cell Foam)

Cause: Open-cell insulation absorbs moisture like a sponge.

Symptoms: Insulation feels wet or spongy, water dripping from insulation, mould or mildew growth.

Solution: Remove open-cell insulation completely and replace with closed-cell elastomeric (K-FLEX ST or SK). Never use open-cell foam on cold pipes.

4. Gaps at Fittings

Cause: Valves, elbows, or tees left uninsulated or poorly insulated.

Symptoms: Condensation at specific fittings, dripping from valves or elbows, bare pipe visible at fittings.

Solution: Insulate ALL fittings completely, use pre-formed valve covers, mitre joints properly at elbows.

5. Damaged Insulation

Cause: Physical damage, UV degradation, or wear has compromised insulation.

Symptoms: Visible tears, cracks, or holes; condensation at damaged areas; insulation has degraded or crumbled.

Solution: Replace damaged sections. Use UV-resistant Solar HT for outdoor pipes. Protect with cladding in high-traffic areas.

6. High Ambient Humidity

Cause: Very high humidity (>70%) overwhelms standard insulation thickness.

Symptoms: Condensation in basements, coastal areas, or plant rooms; worse in summer or humid weather; affects entire system.

Solution: Increase insulation thickness by one size (e.g. 19mm → 25mm, 25mm → 32mm). Improve ventilation if possible.

Diagnostic Checklist

1. Is it closed-cell elastomeric material?
2. Is it thick enough for the application?
3. Are all joints sealed with adhesive?
4. Are valves and elbows fully insulated?
5. Any visible tears, cracks, or degradation?
6. Is ambient humidity very high?

Prevention Tips

• Use closed-cell elastomeric for ALL cold pipes
• Follow thickness guide for application
• Use K-FLEX 800 adhesive or SK self-seal on every joint
• Insulate all fittings — no gaps at valves, elbows, or tees
• Use Solar HT or cladding for outdoor insulation
• Go one size thicker in high-humidity environments

Shop Condensation-Proof Insulation

• K-FLEX ST (Closed-Cell Elastomeric)

Related Guides

• Dew Point & Condensation Explained
• How to Prevent Condensation on Chilled Water Lines
• Insulation Thickness Selection Guide

Still having problems? Contact our technical team for troubleshooting help.