What Thickness Packers Should You Use?
Why Packer Thickness Matters
Choosing the correct packer thickness is one of the most important parts of glazing and frame installation. Using the wrong thickness can cause:
- Frame distortion
- Dropped sashes
- Poor drainage
- Excess pressure on the sealed unit
- Uneven reveal gaps
- Difficulty fitting beads
- Long-term operational issues
Getting the thickness right ensures the window is level, square, well-supported, and sits correctly in the aperture.
Standard Thicknesses (UK Industry Colour Coding)
While manufacturers can vary slightly, the following thickness/colour system is widely accepted in the UK glazing industry:
- 1 mm – Black
- 2 mm – Green
- 3 mm – White
- 4 mm – Blue
- 5 mm – Red
- 6 mm – Yellow
- 10 mm – Brown
Some mixed sets may also include:
- 8 mm
- 12 mm
- 15 mm
But the thicknesses above cover most everyday installations.
When to Use Each Thickness
1 mm Packers (Black)
Use when you need extremely fine adjustment such as:
- Correcting tiny discrepancies
- Micro-level changes on hinges
- Light alignment tweaks
Ideal for final adjustments after the glass is seated.
2 mm Packers (Green)
Commonly used for:
- Slight levelling corrections
- Ensuring consistent reveal gaps
- Balancing minor twists in the frame
Useful when 1 mm is too thin but 3 mm is too thick.
3 mm Packers (White)
A very common thickness for:
- Supporting glass where minor lift is needed
- Maintaining drainage clearance
- Toe-and-heeling non-heavy sashes
This is one of the most frequently used packer sizes.
4 mm Packers (Blue)
Used when the opening requires moderate adjustment:
- Levelling frames on slightly uneven sills
- Balancing sashes during toe-and-heel
- Correcting moderate discrepancies
Often used under the bottom of casements to ensure even support.
5 mm Packers (Red)
Used when you need a noticeable increase in height:
- Supporting heavier sealed units
- Aligning frames in openings with larger variations
- Ensuring consistent margins between sash and frame
Common in situations with uneven brickwork.
6 mm Packers (Yellow)
For larger adjustments where the opening is significantly out of level:
- Supporting big units in wide frames
- Creating larger separation for drainage
- Correcting deeper irregularities in masonry
Often used with aluminium systems that require higher clearances.
8–10 mm Packers (Brown, Grey, etc.)
These are used when major compensation is needed:
- Extremely uneven substrates
- Timber frames with natural variation
- Heavy doors and large glazed panels
- Achieving plumb on significantly out-of-square openings
10 mm packers are also commonly used under frames during installation.
How to Choose the Right Thickness for the Job
Step 1: Measure the Opening and Frame Gaps
Check:
- Bottom level
- Side reveals
- Squareness
- Gap between sash and frame
This determines your starting packer thickness.
Step 2: Support the Glass With Appropriate Bottom Packers
Typical bottom support packers are:
- 4 mm, 5 mm, or 6 mm (depending on system)
- Always used at both bottom corners
The weight of the glass must sit evenly.
Step 3: Toe-and-Heel With Matching or Slightly Different Thicknesses
For side packers used during toe-and-heel:
- Start with 3–5 mm packers
- Adjust based on sash alignment
- Only use wedge packers for micro-adjustments
The goal is to keep the sash square and prevent dropping.
Step 4: Ensure Drainage Channels Are Clear
If drainage channels are tight:
- Use 3 mm or 4 mm packers
- Never use packers thick enough to block water flow
Step 5: Avoid Over-Packing
Using too thick a packer can:
- Push the glass too high
- Create pressure on the sealed unit
- Distort the sash or frame
- Make bead fitting difficult
Only use the thickness required to level, support, and align.
Can You Combine Different Thicknesses?
Yes — installers frequently stack packers to achieve precise spacing.
Examples:
- 4 mm + 2 mm = 6 mm
- 5 mm + 1 mm = 6 mm
- 3 mm + 3 mm = 6 mm
When stacking:
- Make sure surfaces are flat and stable
- Don’t exceed necessary height
- Avoid creating pressure points
Stacking is acceptable, but using a single thickness packer is always preferable if available.
Signs You Used the Wrong Thickness
You may have packed incorrectly if you notice:
- Sash catches when closing
- Lock doesn’t align smoothly
- Uneven gaps around the sash
- Beads won’t snap in easily
- Window appears twisted or bowed
- Visible stress marks on the glass
- Rattling when tapping the glass lightly
All of these are corrected by adjusting packer thickness.
Final Thoughts
Choosing the correct thickness is essential for a long-lasting and smoothly operating window. The right packers ensure proper weight distribution, alignment, drainage, and overall stability.
If you’re stocking up, consider carrying a full range of consistent colour-coded packers: