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uPVC Glazing Packers: Which Sizes Do Installers Actually Use?
For uPVC window and door installation, glazing packers are essential. They help support sealed units, maintain spacing, keep glass properly aligned, and reduce the risk of movement, rattling, gasket stress, or poor fitment.
But one of the most common buying questions is simple:
Which uPVC glazing packer sizes do installers actually use?
The answer depends on the frame system, sealed unit, support point, and job type. However, for regular trade work, most installers should keep a practical range of flat glazing packers, bridge packers, and adjustment packers in stock.
For flat glazing packers, the key sizes to consider are:
- 20mm flat glazing packers
- 24mm flat glazing packers
- 28mm flat glazing packers
These sizes cover a wide range of uPVC window and door glazing work.
Why uPVC Installers Need Different Packer Sizes
uPVC installations are not all the same. Different systems, frame profiles, sealed unit sizes, and site conditions can require different packer widths and thicknesses.
A narrow support point may suit a 20mm flat packer.
A standard everyday job may suit a 24mm flat packer.
A wider system or heavier support point may suit a 28mm flat packer.
The aim is not to force one size into every job. The aim is to keep enough stock so the installer can choose the correct packer on site.
The Main uPVC Glazing Packer Sizes Installers Use
For regular uPVC glazing work, the most useful flat glazing packer widths are usually:
- 20mm
- 24mm
- 28mm
Each width has a different role.
20mm uPVC Glazing Packers
20mm flat glazing packers are useful where the job needs a narrower flat packer.
Installers use them for:
- narrower glazing systems
- compact support points
- standard uPVC window glazing
- door glazing
- conservatory glazing
- smaller support areas
A 20mm packer is useful when a wider 24mm or 28mm packer is not required, or where the available support area is more limited.
24mm uPVC Glazing Packers
24mm flat glazing packers are a strong general-purpose option.
Installers use them for:
- everyday uPVC window installation
- uPVC door glazing
- sealed unit support
- general levelling
- standard spacing work
- conservatories
- curtain walling
The 24mm size sits between 20mm and 28mm, making it a practical middle-ground option for installers who want versatile van stock.
28mm uPVC Glazing Packers
28mm flat glazing packers are useful when the installation needs a wider support surface.
Installers use them for:
- 28mm glazing systems
- larger sealed units
- heavier support points
- uPVC windows and doors
- wider glazing channels
- curtain walling
- conservatories
For installers who regularly handle larger units or wider uPVC systems, 28mm packers should be part of the core stock.
Which Thicknesses Do Installers Actually Use Most?
Across uPVC glazing work, the most useful thicknesses are usually:
- 3mm
- 4mm
- 5mm
These are the main working thicknesses for many everyday installation jobs.
Smaller sizes such as 1mm and 2mm are useful for fine adjustment.
Larger sizes such as 6mm, where available, are useful for larger gaps, base support, and heavier load points.
1mm Packers for Fine Adjustment
1mm packers are used when only a small correction is needed.
Installers use them for:
- final levelling
- fine adjustment
- slight gap removal
- small finishing corrections
They are not usually the main bulk-buying thickness, but they are important to keep available.
2mm Packers for Minor Corrections
2mm packers are used when 1mm is not enough but the job still only needs a light correction.
Installers use them for:
- minor levelling
- small spacing adjustments
- slightly uneven frames
- fine support work
2mm is useful as an adjustment size alongside the main working thicknesses.
3mm Packers for Everyday uPVC Glazing
3mm is one of the most useful thicknesses for regular uPVC glazing work.
Installers use 3mm packers for:
- standard window glazing
- general sealed unit support
- everyday levelling
- routine door glazing
- common installation corrections
For many installers, 3mm should be one of the first thicknesses to keep in bulk.
4mm Packers for Moderate Correction
4mm packers are useful when 3mm does not provide enough correction.
Installers use 4mm packers for:
- moderate gaps
- slightly uneven openings
- supporting heavier sections
- frame or unit alignment
- jobs that need more than standard support
The 4mm size is especially useful in the 24mm and 28mm ranges because it gives installers a middle option between standard 3mm support and stronger 5mm support.
5mm Packers for Stronger Support
5mm packers are used when the job needs stronger support or a larger spacing correction.
Installers use 5mm packers for:
- larger gaps
- heavier sealed units
- stronger support points
- base packing
- more noticeable levelling requirements
For trade buyers, 5mm is one of the most important thicknesses to keep in regular stock.
6mm Packers for Larger Gaps and Base Support
6mm packers are useful where significant correction or support is needed.
Installers use 6mm packers for:
- larger gaps
- uneven openings
- high load-bearing points
- base support
- heavier glazing situations
6mm may not be used on every job, but it is useful to keep available where the installation requires more support.
Which 20mm Thicknesses Should uPVC Installers Stock?
For 20mm flat glazing packers, the available thicknesses are:
- 1mm
- 2mm
- 3mm
- 5mm
A practical 20mm stock setup would be:
- 3mm for everyday support
- 5mm for stronger support
- 1mm and 2mm for fine adjustment
20mm packers are best treated as compact support stock. They are useful where the job calls for a narrower flat packer rather than a wider support surface.
Which 24mm Thicknesses Should uPVC Installers Stock?
For 24mm flat glazing packers, the available thicknesses are:
- 1mm
- 2mm
- 3mm
- 4mm
- 5mm
- 6mm
A practical 24mm stock setup would be:
- 3mm for standard everyday glazing
- 4mm for moderate correction
- 5mm for stronger support
- 1mm and 2mm for fine adjustment
- 6mm for larger gaps and base support
For many installers, 24mm is the most flexible middle option to keep in regular stock.
Which 28mm Thicknesses Should uPVC Installers Stock?
For 28mm flat glazing packers, the available thicknesses are:
- 1mm
- 2mm
- 3mm
- 4mm
- 5mm
- 6mm
A practical 28mm stock setup would be:
- 3mm for standard support
- 4mm for moderate correction
- 5mm for heavier support
- 1mm and 2mm for fine adjustment
- 6mm for larger gaps and base support
For larger uPVC units, wider glazing systems, and stronger support requirements, 28mm packers are especially useful.
Flat Packers vs Bridge Packers for uPVC Windows
Flat glazing packers are useful for general support, spacing, and levelling.
Bridge packers are used where the sealed unit needs support while still allowing drainage and ventilation beneath the glass.
In uPVC glazing work, this distinction matters. If the system requires drainage beneath the sealed unit, a bridge packer may be more suitable than a flat packer.
A practical installer stock setup should usually include both:
- flat glazing packers for general support
- bridge packers where drainage and ventilation need to be maintained
When Installers Should Use MSBP Bridge Packers
For installers working across mixed uPVC systems, MSBP can be useful because it is sold as a multi-system bridge packer for a wide range of compatible uPVC window and door profiles.
It is designed to support glazing units while maintaining drainage and ventilation beneath sealed units.
MSBP is worth considering when:
- you work across multiple uPVC systems
- you want to reduce the need for several profile-specific bridge packers
- drainage and ventilation beneath the sealed unit matter
- you want simpler van stock for compatible systems
- you regularly handle uPVC window and door glazing
Installers should always confirm suitability for the specific profile and installation before use.
Should uPVC Installers Carry Wedge Packers Too?
Yes, wedge packers are useful alongside flat and bridge packers.
Wedge packers are not the main support packer for every job, but they are useful for:
- fine adjustment
- small alignment corrections
- levelling
- positioning during fitting
- finishing adjustments
For a proper uPVC glazing kit, installers should usually carry flat packers, bridge packers, and wedge packers.
Recommended uPVC Glazing Packer Stock for Installers
A practical uPVC glazing packer stock setup would include:
- 20mm flat glazing packers in 3mm and 5mm
- 24mm flat glazing packers in 3mm, 4mm, and 5mm
- 28mm flat glazing packers in 3mm, 4mm, and 5mm
- 1mm and 2mm options for fine adjustment
- 6mm options where available for larger gaps and base support
- bridge packers for suitable uPVC systems
- wedge packers for fine adjustment
This gives installers a strong working range without relying on one size for every job.
Recommended Stock for Self-Employed uPVC Installers
For a self-employed installer, a sensible starting setup would be:
- 20mm 3mm and 5mm
- 24mm 3mm, 4mm, and 5mm
- 28mm 3mm, 4mm, and 5mm
- small stock of 1mm and 2mm
- 6mm where available
- bridge packers
- wedge packers
This gives enough flexibility for most regular uPVC window and door jobs.
Recommended Stock for Larger Installation Teams
For companies with multiple installers, stock should be more structured.
A practical setup would be:
- higher stock of 24mm 3mm, 4mm, and 5mm
- higher stock of 28mm 3mm, 4mm, and 5mm
- regular stock of 20mm 3mm and 5mm
- lower but available stock of 1mm and 2mm
- 6mm for larger gaps and base support
- MSBP or other bridge packers for suitable systems
- wedge packers for adjustment
This helps keep every van stocked consistently and reduces last-minute ordering.
Common Mistakes When Buying uPVC Glazing Packers
Avoid these common mistakes:
- buying only one packer width
- buying only one thickness
- using flat packers where bridge packers are required
- not keeping 1mm and 2mm adjustment sizes
- not stocking 4mm and 5mm for stronger support
- using 20mm when the job needs a wider support area
- using 28mm when a narrower packer would fit better
- relying on timber, cardboard, or improvised shims
The correct packer should match the uPVC system, the sealed unit, and the support requirement.
Which Sizes Should You Buy First?
If you are starting from scratch, prioritise the most commonly useful working sizes first.
Start with:
- 24mm 3mm
- 24mm 4mm
- 24mm 5mm
- 28mm 3mm
- 28mm 4mm
- 28mm 5mm
- 20mm 3mm
- 20mm 5mm
Then add:
- 1mm and 2mm for fine adjustment
- 6mm where available for larger gaps
- bridge packers for compatible uPVC systems
- wedge packers for adjustment
This gives you a practical stock range that supports real installation work rather than just filling the van with random sizes.
Final Thoughts
uPVC installers use different glazing packer sizes depending on the frame system, sealed unit, and support requirement.
For flat glazing packers, the key widths to keep in stock are:
- 20mm for narrower support points
- 24mm for general-purpose uPVC glazing work
- 28mm for wider systems and stronger support
For thicknesses, the most useful working sizes are usually:
- 3mm
- 4mm
- 5mm
Then keep:
- 1mm and 2mm for fine adjustment
- 6mm where available for larger gaps and base support
For a complete uPVC glazing setup, installers should also carry bridge packers where drainage and ventilation beneath the sealed unit matter, plus wedge packers for fine adjustment.
Explore our uPVC glazing packer range: