How to identify single, double, or high-efficiency glazing?

At Group Ceyssens, we focus entirely on total renovations where

Would you like to know if your windows qualify for an upgrade to high-efficiency glass? Or are you looking to replace the existing panes in your home? In that case, it is important to first determine which type of glass is currently installed in your windows. At Group Ceyssens, we focus entirely on total renovations where the existing window profiles are retained and only the glass is replaced. We do not perform any modifications or replacements of window profiles. To ensure every project starts correctly, we first conduct a thorough analysis of the existing situation. This allows us to know exactly what is possible and how to achieve the best result. With a few simple checks, you can determine which type of glass is currently in your windows and whether your project aligns with our approach.

Single or double glazing? The difference is often immediately apparent

First, look at the side of the window. Do you see a single glass panel? Then you have single glazing. If you see two glass panels with a small space between them, it is double glazing or high-efficiency glass. These two glass layers are separated by a spacer, often an aluminium, plastic, or Polymer (= Super Spacer Edgetech; high thermal properties tailored to current and future insulation standards) edge that seals the space between the glass panels.

Note the markings in the profile

There is usually a spacer between the glass layers. Technical information is often printed on it, such as:

the name of the glass manufacturer
the year of production
an indication of the glass type, such as HR, HR+, or HR++

The ‘lighter trick’: a visual test

A simple way to check the type of glass is with a lit lighter (or match). Hold the flame close to the window and look at the reflections in the glass from an angle:

2 flames? → Single glazing
4 flames? → Double or high-efficiency glazing

Then look at the colour of the flames:

All the same colour? → Double glazing
Does one of the flames have a different colour (e.g., blue or purple)? → High-efficiency glass with coating

An overview

Glass type	How to identify?	What does it mean?
Single glazing	One glass pane	Minimal insulation, energy costs are higher
Double glazing	Two panes, identical reflection colours	Better insulation, traditionally common
HR / HR++ glass	Four reflections, different colour	High insulation thanks to coating and gas filling
Low-E	Subtle colour effects, cool to the touch	Extra thermal comfort – like a glass mantle for your home

Ready for an upgrade?