Flat vs Wedge Packers: What’s the Difference and When to Use Each?
When installing windows, doors, or any framed structure, the type of packer you choose makes a big difference to the final alignment, long-term stability, and overall installation quality. Two of the most commonly used types are flat packers and wedge packers—each designed for different situations.
In this guide, we’ll compare the two, explain how they work, and help you choose the correct packer for your next installation.
What Are Flat Packers?
Flat packers are rectangular plastic spacers with a uniform thickness across their entire surface.
They are the most widely used packers in the glazing industry.
Common Uses for Flat Packers
Installers use flat packers to:
- Level and align window and door frames
- Support double- or triple-glazed units
- Create consistent gaps around the frame
- Maintain drainage pathways
- Prevent frame distortion
- Correct racked, twisted, or bowed openings
Flat packers are available in industry-standard colour-coded thicknesses (1mm to 10mm+), giving installers predictable, accurate spacing.
Advantages of Flat Packers
- Provide stable, even support
- Work for almost all general glazing and carpentry tasks
- Maintain consistent spacing under loads
- Ideal for supporting glass without creating pressure points
Flat packers are the default choice in most installations.
What Are Wedge Packers?
Wedge packers—also called tapered packers—are angled or sloped packers that gradually increase in height from one end to the other.
They are designed for fine adjustments in situations where flat packers alone cannot achieve the right angle or level.
Common Uses for Wedge Packers
Wedge packers are ideal for:
- Fine-tuning levels where the cavity isn’t perfectly square
- Making micro-adjustments (where an extra 1mm makes a difference)
- Aligning frames on uneven masonry
- Correcting slight installation variances
- Achieving alignment where small changes dramatically affect operation (e.g., doors that rub, windows that catch)
Advantages of Wedge Packers
- Provide incremental height adjustment
- Allow perfect levelling on uneven surfaces
- Offer precision where multiple flat packers would be too thick
- Allow quick on-site corrections during fitting
Wedge packers shine in non-uniform or irregular openings.
Flat vs Wedge Packers: Key Differences
| Feature | Flat Packers | Wedge Packers |
|---|---|---|
| Shape | Uniform thickness | Tapered/angled |
| Adjustment | Fixed spacing | Adjustable, micro-level adjustments |
| Best Use Case | Standard glazing support | Uneven surfaces, fine tuning |
| Pressure Distribution | Very even | Slightly concentrated due to taper |
| Common Applications | Supporting glass, levelling frames | Correcting misalignment or uneven gaps |
| Precision | Good | Excellent |
Both packer types are necessary—but used for different reasons.
When to Use Flat Packers
Use flat packers when:
✔ You need solid, even support
✔ You’re installing glass units
✔ The aperture is level and square
✔ You want to set the exact thickness
✔ You’re packing under hinges or fixing points
✔ You’re maintaining drainage gaps
Ideal for:
- uPVC window installation
- Aluminium frame installation
- Door frames
- Internal joinery
- Kitchens, cabinets, flooring
Flat packers should be your go-to for 99% of regular installations.
When to Use Wedge Packers
Use wedge packers when:
✔ The opening is uneven or out of square
✔ You need precise height adjustments
✔ A small change fixes a larger alignment problem
✔ You’re aligning frames on rough or inconsistent brickwork
✔ You need to lift one side slightly to prevent rubbing
✔ You need to adjust reveals or make a frame perfectly plumb
Ideal for:
- Frames installed on uneven sills
- Doors that rub or catch during operation
- Windows not closing tightly due to slight misalignment
- Installations with variable gaps or inconsistent masonry
Wedge packers are perfect for precision alignment.
Can You Use Flat and Wedge Packers Together?
Yes—many installers combine both types when needed.
Example situations:
- Use a flat packer for the main support under glass
- Add a wedge packer on one side to adjust level
- Use a combination when fixing timber frames with small discrepancies
- Stack a flat packer under a wedge to increase height range
Using them together provides maximum flexibility during installation.
Which Type Should You Buy?
If you’re an installer, the best solution is to have both:
Flat packers:
Your everyday essential for general glazing and support.
Wedge packers:
Your precision tool for fine adjustments and correcting irregularities.
Most professionals carry:
- A selection box of flat packers (1mm – 10mm)
- 2–3 sets of wedge packers for alignment tasks
This combination covers nearly every installation scenario.
Final Thoughts
Flat packers and wedge packers are both indispensable tools in the glazing and joinery industry. Flat packers offer stable, predictable support, while wedge packers provide fine adjustments when accuracy matters most.
Knowing when to use each one ensures:
- Correct alignment
- Smooth operation of windows and doors
- Reduced risk of glass stress or cracking
- Long-lasting, trouble-free installations
For installer-grade packers, you can explore: