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Glazing Packers for Windows: What to Buy for uPVC, Aluminium and Timber Frames
When buying glazing packers for windows, the right choice depends on more than just thickness. Installers also need to consider the frame material, the glazing system, the support area, and whether the job needs flat packers, bridge packers, or wedge packers.
A packer that works well in one window system may not be the best choice for another. uPVC, aluminium, and timber frames all have different fitting requirements, which is why professional installers should keep a practical range of glazing packers in stock.
At GlazingPacker, we stock flat glazing packers in key trade sizes, including 20mm, 24mm, and 28mm, with multiple thickness options for different installation needs.
Why the Frame Material Matters
Glazing packers are used to support, level, and position sealed glass units inside the frame. Their job is to help keep the unit square, stable, and correctly aligned.
But different frame materials can affect the type of packer an installer should choose.
A uPVC frame may require attention to drainage, ventilation, and profile compatibility.
An aluminium frame may need accurate support and careful spacing because the systems are often more precise and rigid.
A timber frame may require stable, non-compressible support because the frame material can behave differently from plastic or metal over time.
The correct packer should match the frame, the glass unit, and the installation method.
The Main Glazing Packer Types for Window Installation
For window work, installers usually need three main product types:
Each type has a different role.
Flat glazing packers are used for general support, spacing, and levelling.
Bridge packers are used where drainage and ventilation beneath the sealed unit must be maintained.
Wedge packers are useful for fine adjustment and positioning.
For most window installers, flat glazing packers are the main product to buy first. Bridge and wedge packers should then be added depending on the frame system and type of work.
What Flat Glazing Packers Should You Buy?
For flat glazing packers, the main sizes to consider are:
These sizes cover a wide range of window and door glazing work.
As a simple buying guide:
- choose 20mm for narrower systems and compact support points
- choose 24mm for general-purpose glazing work
- choose 28mm for wider support areas and heavier glazing jobs
For trade buyers, it usually makes sense to keep all three sizes available rather than relying on one width for every job.
Glazing Packers for uPVC Windows
uPVC windows are one of the most common uses for glazing packers. Installers need packers to support sealed units, maintain correct spacing, help with alignment, and keep the glass properly positioned in the frame.
For uPVC windows, the best stock setup usually includes:
- flat glazing packers for general support
- bridge packers where drainage and ventilation beneath the sealed unit matter
- wedge packers for adjustment
The main flat packer sizes to consider are 20mm, 24mm, and 28mm.
What to Buy for uPVC Windows
For uPVC window installation, we recommend keeping:
- 20mm flat glazing packers for narrower support points
- 24mm flat glazing packers for general uPVC glazing work
- 28mm flat glazing packers for wider systems and heavier support requirements
- bridge packers for suitable uPVC systems where drainage and ventilation are important
- wedge packers for fine adjustment
If you install uPVC windows regularly, 24mm and 28mm flat glazing packers are likely to be the most useful core stock, with 20mm kept for narrower or more compact support areas.
When to Use Bridge Packers for uPVC Windows
Bridge packers are especially important in suitable uPVC window systems because they support the sealed unit while allowing drainage and ventilation beneath the glass.
If a uPVC system requires drainage below the sealed unit, a standard flat packer may not always be the right choice. A bridge packer helps maintain the required space under the glass.
For installers working across mixed uPVC systems, MSBP can be useful because it is sold as a multi-system bridge packer for compatible uPVC window and door profiles.
Glazing Packers for Aluminium Windows
Aluminium window systems often require accurate, stable packing because the frames are usually rigid and the tolerances can be tighter than some other systems.
For aluminium windows, the correct glazing packer helps maintain proper support and spacing without putting unnecessary stress on the glass unit.
Flat glazing packers are commonly used for aluminium frames because they give consistent, non-compressible support.
What to Buy for Aluminium Windows
For aluminium window installation, we recommend keeping:
- 24mm flat glazing packers for general-purpose aluminium glazing work
- 28mm flat glazing packers where a wider support surface is needed
- 20mm flat glazing packers for narrower support areas
- 1mm and 2mm packers for fine adjustment
- 3mm, 4mm, and 5mm packers for regular support
- 6mm where available for larger gaps or stronger support
Aluminium installations often benefit from having fine adjustment sizes available because small differences in spacing can affect the fit and alignment.
Glazing Packers for Timber Windows
Timber frames are different from uPVC and aluminium because wood can respond to moisture, movement, and site conditions over time. That makes stable, consistent support important.
Plastic glazing packers are useful for timber frames because they provide a consistent thickness and do not behave like improvised timber shims or cardboard packing.
For timber windows, flat glazing packers are often the main product to buy.
What to Buy for Timber Windows
For timber window installation, we recommend keeping:
- 20mm flat glazing packers where the frame or support area is narrower
- 24mm flat glazing packers for general timber glazing work
- 28mm flat glazing packers for wider support points or heavier sealed units
- 3mm and 5mm as core working thicknesses
- 1mm and 2mm for fine adjustment
- 4mm and 6mm where available for moderate or larger corrections
For many timber installations, the correct thickness matters as much as the width. The aim is to support the sealed unit properly without forcing the frame or creating uneven pressure.
Which Width Should You Buy First?
For most installers, the best starting point is not one single width. A practical stock setup should include 20mm, 24mm, and 28mm flat glazing packers.
However, if you want to prioritise, use this guide:
Buy 20mm Flat Glazing Packers If
Choose 20mm flat glazing packers if you work with:
- narrower glazing systems
- compact support points
- smaller support areas
- standard window and door glazing where a wider packer is not required
20mm is useful when space is limited or when a narrower flat packer is more appropriate.
Buy 24mm Flat Glazing Packers If
Choose 24mm flat glazing packers if you want a versatile middle option.
24mm is useful for:
- general uPVC window installation
- aluminium frames
- timber frames
- standard sealed unit support
- everyday glazing work
For many installers, 24mm is the safest general-purpose size to keep in regular stock.
Buy 28mm Flat Glazing Packers If
Choose 28mm flat glazing packers if you work with:
- wider glazing systems
- larger sealed units
- heavier support points
- curtain walling
- bigger window and door installations
28mm is useful when the job needs a wider support surface or stronger load distribution.
Which Thicknesses Should You Buy?
Once you choose the correct width, the next step is choosing the thickness.
For most window installation work, the most useful thicknesses are:
- 3mm
- 4mm
- 5mm
These are the main working sizes for regular support and correction.
You should also keep:
- 1mm for fine adjustment
- 2mm for minor correction
- 6mm where available for larger gaps and heavier support
1mm Packers
Use 1mm packers for fine adjustment and final levelling.
They are useful when the glass unit is already close to the correct position and only needs a small correction.
2mm Packers
Use 2mm packers for light correction.
They are useful for minor spacing adjustments and small inconsistencies in the frame or opening.
3mm Packers
Use 3mm packers for everyday window installation work.
This is one of the most useful general-purpose thicknesses for sealed unit support and standard levelling.
4mm Packers
Use 4mm packers for moderate correction.
This thickness is useful when 3mm is not enough, especially in 24mm and 28mm flat glazing packers.
5mm Packers
Use 5mm packers for stronger support and larger gaps.
This is one of the most useful trade thicknesses for installers working across different frame materials.
6mm Packers
Use 6mm packers where available for larger gaps, base support, or heavier load points.
They may not be needed on every job, but they are important to keep available for more demanding installations.
Recommended Stock for uPVC, Aluminium and Timber Installers
If you work across uPVC, aluminium, and timber windows, a practical 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 for fine adjustment
- 6mm where available for larger gaps and stronger support
- bridge packers for suitable uPVC systems
- wedge packers for fine adjustment
This gives installers enough flexibility to handle different frame materials without carrying unnecessary stock.
Recommended Stock for uPVC Specialists
If you mainly work on uPVC windows, prioritise:
- 24mm flat glazing packers
- 28mm flat glazing packers
- 20mm flat glazing packers for narrower support points
- bridge packers for compatible uPVC systems
- wedge packers for adjustment
For thicknesses, focus on:
- 3mm
- 4mm
- 5mm
Then keep 1mm, 2mm, and 6mm available for specific jobs.
Recommended Stock for Aluminium Window Installers
If you mainly work on aluminium windows, prioritise:
- 24mm flat glazing packers for general work
- 28mm flat glazing packers for wider support points
- 1mm and 2mm for precise adjustment
- 3mm, 4mm, and 5mm for regular support
Aluminium work often benefits from accurate spacing, so do not ignore the smaller adjustment sizes.
Recommended Stock for Timber Window Installers
If you mainly work on timber windows, prioritise:
- 24mm flat glazing packers for general glazing support
- 28mm flat glazing packers for larger units
- 20mm flat glazing packers for narrower frame areas
- 3mm and 5mm as core working sizes
- 1mm and 2mm for fine adjustment
The key is to use proper plastic packers rather than improvised timber or cardboard shims.
Why Installers Should Not Use One Packer for Every Frame
One of the biggest mistakes is using the same packer size for every job.
That may seem simpler, but it can cause problems.
If the packer is too narrow, it may not give the support area needed.
If the packer is too wide, it may be awkward to place or unnecessary for the frame.
If the thickness is wrong, the glass unit may not sit correctly.
The better approach is to carry a working range and choose the correct packer based on the frame and sealed unit.
Why Plastic Packers Are Better Than Improvised Shims
Some installers still use timber offcuts, cardboard, or other materials as makeshift packers. That may seem convenient, but it is not ideal for professional window installation.
Purpose-made plastic glazing packers offer:
- consistent thickness
- predictable support
- moisture resistance
- faster size identification
- cleaner installation
- better long-term stability
For uPVC, aluminium, and timber frames, using the correct plastic glazing packer is a more professional and reliable choice.
Common Buying Mistakes to Avoid
When buying glazing packers for windows, avoid these mistakes:
- buying only one width
- buying only one thickness
- using flat packers where bridge packers are needed
- ignoring fine adjustment sizes
- using 20mm when the job needs wider support
- using 28mm where a narrower packer would fit better
- relying on timber, cardboard, or offcuts
- not keeping enough stock in the van
Good stock planning helps reduce installation delays and prevents poor product selection on site.
Final Thoughts
The best glazing packers for windows depend on whether you are working with uPVC, aluminium, or timber frames.
For most installers, the core flat glazing packer sizes to keep in stock are:
- 20mm for narrower support points
- 24mm for general-purpose window glazing
- 28mm for wider systems and heavier support requirements
For thicknesses, prioritise:
- 3mm
- 4mm
- 5mm
Then keep:
- 1mm and 2mm for fine adjustment
- 6mm where available for larger gaps or stronger support
If you install uPVC windows, also keep bridge packers available where drainage and ventilation beneath the sealed unit matter. If you work across multiple uPVC systems, MSBP may help reduce the number of bridge packer types you need to carry.
Explore our glazing packer range: