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20mm vs 24mm vs 28mm Flat Glazing Packers: Which Size Should You Buy?
When buying flat glazing packers, most installers focus on thickness first. That makes sense, because the thickness controls the amount of lift, spacing, or support you get on the job.
But the width of the packer matters too.
A 20mm, 24mm, and 28mm flat glazing packer may look similar at first, but each size is suited to slightly different glazing systems, frame setups, and support requirements. Choosing the correct width helps the packer sit properly, support the sealed unit correctly, and fit the system without creating unnecessary pressure or obstruction.
At GlazingPacker, we stock 20mm, 24mm, and 28mm flat glazing packers in trade packs, giving installers a practical choice depending on the glazing system they are working with.
Quick Comparison: 20mm vs 24mm vs 28mm Flat Glazing Packers
Here is a simple way to understand the difference:
| Packer size | Best for | Available thicknesses |
|---|---|---|
| 20mm flat glazing packers | Narrower glazing systems, compact support points, standard window and door glazing | 1mm, 2mm, 3mm, 5mm |
| 24mm flat glazing packers | General glazing work across uPVC, aluminium, and timber frames | 1mm, 2mm, 3mm, 4mm, 5mm, 6mm |
| 28mm flat glazing packers | Wider glazing systems, heavier support points, larger windows and door installations | 1mm, 2mm, 3mm, 4mm, 5mm, 6mm |
The easiest way to decide is to match the packer width to the glazing system and then choose the thickness based on the amount of support or correction required.
When Should You Buy 20mm Flat Glazing Packers?
Choose 20mm flat glazing packers when the installation needs a narrower flat packer but still requires firm, stable support.
Our 20mm flat glazing packers are useful for:
- 20mm glazing systems
- standard window and door glazing
- compact support points
- sealed unit alignment
- conservatory glazing
- uPVC, aluminium, and timber frames
The 20mm size is especially practical when a wider packer may be unnecessary or where the available space in the system is more limited.
Best Thicknesses to Buy in 20mm Flat Glazing Packers
Our 20mm flat glazing packers are available in:
- 1mm
- 2mm
- 3mm
- 5mm
For most trade buyers, the key thicknesses are likely to be 3mm and 5mm.
Use 3mm for standard everyday glazing support. This is the all-round working thickness for many window and door jobs.
Use 5mm where the job needs more spacing, stronger support, or base packing.
The 1mm and 2mm options are useful for fine adjustment and light correction, but most installers will usually use them as support sizes rather than main bulk-buying sizes.
When Should You Buy 24mm Flat Glazing Packers?
Choose 24mm flat glazing packers when you want a strong general-purpose flat packer for everyday glazing work.
This is a very useful middle option between 20mm and 28mm. It gives more width than a 20mm packer, but it is not as wide as a 28mm packer. For many installers, 24mm is a practical everyday choice across a wide range of frames.
Our 24mm flat glazing packers are useful for:
- 24mm glazing systems
- uPVC window and door installations
- aluminium and timber frames
- sealed glass units
- curtain walling
- conservatories
- general levelling and support work
If you are not sure whether to stock 20mm or 28mm in higher volume, 24mm can be a sensible middle-ground option for general glazing work.
Best Thicknesses to Buy in 24mm Flat Glazing Packers
Our 24mm flat glazing packers are available in:
- 1mm
- 2mm
- 3mm
- 4mm
- 5mm
- 6mm
For trade buyers, the most useful 24mm thicknesses are usually:
- 3mm
- 4mm
- 5mm
Use 3mm for standard everyday glazing support.
Use 4mm where the installation needs moderate correction or a little extra support.
Use 5mm where the job involves larger spacing requirements, heavier sealed units, or stronger support points.
The 6mm option is useful when greater spacing or base support is required, while 1mm and 2mm are best kept for fine adjustment and smaller corrections.
When Should You Buy 28mm Flat Glazing Packers?
Choose 28mm flat glazing packers when the installation needs a wider support surface or when you are working with 28mm glazing systems.
The 28mm size is especially useful for installers who regularly work on wider glazing setups, heavier sealed units, or jobs where stronger support and load distribution are important.
Our 28mm flat glazing packers are useful for:
- 28mm glazing systems
- uPVC, aluminium, and timber installations
- windows and doors
- sealed glass units
- curtain walling
- conservatories
- larger or more demanding glazing work
If your jobs regularly involve larger units or wider glazing channels, 28mm flat glazing packers are likely to be one of the most important sizes to keep in stock.
Best Thicknesses to Buy in 28mm Flat Glazing Packers
Our 28mm flat glazing packers are available in:
- 1mm
- 2mm
- 3mm
- 4mm
- 5mm
- 6mm
For most installers, the core 28mm trade sizes are:
- 3mm
- 4mm
- 5mm
Use 3mm for standard glazing support and general window installations.
Use 4mm for moderate gaps, slightly misaligned frames, or heavier sections.
Use 5mm where stronger support is required, especially for heavier sealed units or larger gaps.
The 6mm option is useful for high load-bearing points, base packing, and more noticeable correction, while 1mm and 2mm are useful for fine levelling and smaller adjustments.
Which Size Should You Buy First?
If you are buying flat glazing packers for general stock, the best choice depends on the type of work you do.
Buy 20mm flat glazing packers if:
- you work with narrower glazing systems
- you need compact support points
- you want a simple range for standard window and door glazing
- you mainly need 3mm and 5mm stock
Buy 24mm flat glazing packers if:
- you want a versatile middle option
- you work across uPVC, aluminium, and timber frames
- you need a full 1mm to 6mm thickness range
- you want a practical general-purpose packer
Buy 28mm flat glazing packers if:
- you work with 28mm glazing systems
- you need a wider support surface
- you handle larger sealed units or heavier glazing jobs
- you want a strong trade stock option for windows, doors, and curtain walling
What Should Trade Installers Keep in Stock?
For professional installers, the best approach is usually not to choose only one size. Most trade buyers are better off keeping a working stock of all three sizes:
- 20mm for narrower systems and compact support points
- 24mm for general-purpose glazing work
- 28mm for wider systems and heavier support requirements
Within each size, the most useful thicknesses are usually the middle options.
For regular trade stock, a practical starting setup would be:
- 20mm: 3mm and 5mm
- 24mm: 3mm, 4mm, and 5mm
- 28mm: 3mm, 4mm, and 5mm
Then keep smaller quantities of 1mm and 2mm for fine adjustment, and 6mm in the 24mm and 28mm ranges for larger gaps or heavier support work.
Why Buying the Right Size Reduces Wasted Stock
Buying the wrong flat glazing packers can create two problems.
First, the packer may not suit the system properly. If it is too narrow, it may not provide the support you want. If it is too wide, it may be awkward to position or unnecessary for the job.
Second, you may end up with slow-moving stock. For example, if your work mainly involves standard uPVC window installations, you may use 24mm and 28mm packers more often than very narrow or specialist options. If you handle compact systems, then 20mm may move faster.
The aim is to match your buying pattern to the work you actually do.
A Simple Buying Rule
If you want a simple rule:
- Choose 20mm for narrower or more compact glazing systems.
- Choose 24mm for everyday general glazing work.
- Choose 28mm for wider systems, heavier units, and stronger support requirements.
Then choose the thickness based on the correction needed:
- 1mm–2mm for fine adjustment
- 3mm for standard everyday support
- 4mm–5mm for moderate to stronger correction
- 6mm for larger gaps and heavier support, where available
This gives installers a clear way to buy the right product without overcomplicating the decision.
Final Thoughts
When choosing between 20mm, 24mm, and 28mm flat glazing packers, the right choice depends on the glazing system, the available space, and the level of support required.
For compact or narrower installations, choose 20mm flat glazing packers.
For a versatile everyday option, choose 24mm flat glazing packers.
For wider glazing systems and heavier support requirements, choose 28mm flat glazing packers.
For trade buyers, the strongest stock strategy is to keep all three sizes available, with the biggest focus on commonly used thicknesses such as 3mm, 4mm, and 5mm. That gives installers the flexibility to handle different glazing systems properly while reducing delays, mistakes, and wasted site time.
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