How to Choose the Right Glazing Packers for Window Installation

Glazing packers might be small, but choosing the wrong type or size can cause major problems — from rattling glass to water ingress and failed frames. This guide covers everything you need to know to pick the right packer for every job.

What Are Glazing Packers?

Glazing packers (also called setting blocks, shimming packers, or glass packers) are small plastic blocks used to position and support glass or frames during installation. They ensure the glass sits square and level, bear the load correctly, and leave the correct clearance for sealants and drainage.

The Main Types of Glazing Packer

Flat Packers

Flat packers are the most commonly used type. They come in standard widths (typically 28mm, 30mm, and 32mm) and a range of thicknesses — usually 1mm, 2mm, 3mm, 4mm, 5mm, and 6mm. Most quality flat packers are colour-coded by thickness so you can identify the right size at a glance on site.

When to use: General purpose glazing and frame levelling where you need a known, precise thickness.

Bridge Packers

Bridge packers (also called horseshoe packers) have an open slot that allows them to be slid around a bead or frame member rather than placed underneath it. They are available in 15mm, 20mm, and 28mm widths.

When to use: Toe and heel glazing — positioning glass within the frame to control load distribution. The open bridge shape makes them ideal for fitting in tight spaces without removing the glass.

Wedge Packers

Wedge packers are tapered, allowing them to be driven into a gap to create a tight, adjustable fit. They are particularly useful for levelling cills and sills where the gap varies.

When to use: Frame installation over uneven surfaces; cill and threshold levelling.

U Packers

U-shaped packers that clip around a profile or bead for quick, secure placement.

When to use: Quick placement around profiles; scenarios where access is limited.

Choosing the Right Thickness

The correct packer thickness depends on the clearance required by the frame and glass specification. As a general rule:

• Check the frame manufacturer's installation guide for recommended clearances
• Use the thinnest combination of packers that achieves the required height — stacking multiple thin packers is better than using a single thick one that may crush or creep
• Colour-coded packs make it easy to select the right thickness: check the manufacturer's colour code chart

How Many Packers Do I Need?

For a standard domestic window, you will typically need:

• 2 toe packers and 2 heel packers per pane
• Additional packers for larger or heavier units
• Side packers as specified by the frame manufacturer

For high-rise or commercial installations, always refer to the specific project specification.

Material Matters

Quality glazing packers are made from high-impact polystyrene (HIPS) or polypropylene. Avoid cheap packers that can compress, crack, or degrade over time — these can lead to glass movement, seal failure, and costly remedial work.

All glazing packers from Glazing Supplies Direct are manufactured to high tolerances and are resistant to moisture, UV, and the temperature extremes common on UK construction sites.

Summary

Browse our full range of glazing packers and bridge packers, or contact us if you need advice on a specific application.