20mm Glazing Packers: When Should Installers Use Narrow Flat Packers?

Not every glazing job needs the widest flat packer available. In some window and door installations, a narrower flat glazing packer is the more practical choice because the support area is more compact, the glazing system is narrower, or the installer needs accurate support without using a wider packer than necessary.

That is where 20mm flat glazing packers are useful.

At GlazingPacker, we stock 20mm × 100mm flat glazing packers for installers who need a compact, trade-ready packer for 20mm glazing systems and narrower support points.

What Are 20mm Glazing Packers?

20mm glazing packers are flat plastic packers used to support, level, and space sealed units within the frame. They are narrower than 24mm and 28mm flat glazing packers, making them useful where the installation calls for a more compact flat support.

They are commonly used for:

• glazed units
• window and door glazing
• conservatories
• curtain walling
• uPVC frames
• aluminium frames
• timber frames

Their role is to keep the glazed unit properly supported, correctly aligned, and stable within the frame.

Why Installers Use Narrow Flat Packers

Installers use narrow flat packers when the job needs controlled support in a smaller or more restricted area.

A wider packer is not always the better choice. If the frame, glazing channel, or support point is more compact, a narrower packer can be easier to position and more appropriate for the system.

20mm flat glazing packers are useful when you want:

• a narrower support width
• clean placement in compact areas
• reliable load support
• accurate levelling
• consistent spacing
• a practical packer for 20mm glazing systems

The key is to match the packer to the system, not simply choose the widest option by default.

When Should You Use 20mm Flat Glazing Packers?

Use 20mm flat glazing packers when the installation calls for a narrower flat packer but still needs proper support.

They are especially useful when:

• the glazing system is designed around 20mm support points
• the frame has limited available space
• a wider flat packer is not required
• the job needs compact but stable support
• the installer wants a clean fit without excess width
• the sealed unit needs levelling or spacing in a narrower channel

For installers working across different frame systems, 20mm packers are worth keeping in stock because they fill a useful gap between very small packers and wider 24mm or 28mm options.

When 20mm Packers Are Better Than Wider Packers

20mm packers are often the better choice when the available support area is narrower.

For example, if a 24mm or 28mm packer feels unnecessarily wide for the frame section, a 20mm packer may sit more naturally in the space. This can make the installation cleaner and reduce the need to force a wider packer into an area where it does not really belong.

A 20mm flat packer is not “weaker” simply because it is narrower. It is a different size for a different fitting situation.

When You Should Consider 24mm or 28mm Instead

20mm flat glazing packers are not the right choice for every job.

If the installation needs a wider support surface, a wider glazing system, or a broader base for heavier support, then 24mm or 28mm flat glazing packers may be more suitable.

As a simple guide:

• use 20mm for narrower systems and compact support points
• use 24mm for general-purpose glazing work
• use 28mm for wider systems and larger support areas

The best installers keep more than one width available so they can choose the correct packer for the actual frame and job.

Available Thicknesses in 20mm Glazing Packers

Our 20mm flat glazing packers are available in:

• 1mm
• 2mm
• 3mm
• 5mm

This gives installers a compact but practical range for fine adjustment, standard support, and heavier correction work.

When to Use 1mm 20mm Glazing Packers

Use 1mm 20mm glazing packers when the installation only needs a very small adjustment.

They are useful for:

• final alignment
• fine levelling
• removing very small gaps
• small finishing corrections after main packing

This is the thickness to use when the unit is already close to the correct position and you only need a light adjustment.

When to Use 2mm 20mm Glazing Packers

Use 2mm 20mm glazing packers for minor correction and light support.

They are useful for:

• slightly uneven surfaces
• small spacing corrections
• light levelling under glazing units
• minor frame inconsistencies

2mm is a useful step up from 1mm when a fine adjustment is not enough but the job still does not need a standard or heavy support packer.

When to Use 3mm 20mm Glazing Packers

Use 3mm 20mm glazing packers for standard everyday glazing work.

They are useful for:

• typical window glazing
• door glazing
• standard levelling
• general-purpose support
• everyday sealed unit positioning

For most installers, 3mm is likely to be the most useful working thickness in the 20mm range.

When to Use 5mm 20mm Glazing Packers

Use 5mm 20mm glazing packers when the job needs more support or a larger spacing correction.

They are useful for:

• larger gaps
• heavier sealed units
• structural support points
• base packing
• stronger correction in compact areas

5mm is the heavier support option in the 20mm range and is worth keeping in stock if you regularly handle more demanding window or door glazing work.

Why 20mm Packers Are Useful for Van Stock

20mm flat glazing packers are useful for van stock because they cover jobs where a narrower packer is required but proper flat support is still needed.

A practical 20mm van stock setup would include:

• 3mm for everyday glazing work
• 5mm for stronger support and larger gaps
• 1mm and 2mm for fine adjustment and light correction

This gives installers enough flexibility to deal with most compact 20mm packer applications without carrying unnecessary stock.

Why Installers Should Not Use One Width for Every Job

One common mistake is using the same flat packer width on every installation. That may seem simpler, but it can lead to poor product selection.

If the packer is too narrow, it may not give the support area the installer wants.

If the packer is too wide, it may be awkward to position or unnecessary for the system.

The better approach is to carry a selection of widths and use the one that suits the job.

20mm flat glazing packers are part of that professional stock setup.

Why Installers Should Not Use Improvised Narrow Packers

Some installers may try to create a narrow shim using offcuts, timber, cardboard, or leftover material. That is not a good substitute for proper plastic glazing packers.

Purpose-made 20mm plastic glazing packers give installers:

• consistent thickness
• predictable support
• clean placement
• better long-term stability
• faster identification on site
• a more professional installation method

For trade work, proper packers are a small cost compared with the cost of callbacks, rework, or poor fitment.

Common Mistakes When Using 20mm Glazing Packers

Avoid these common mistakes:

• using 20mm packers where a wider support surface is needed
• using 1mm or 2mm when the job clearly needs stronger support
• using 5mm where only a fine adjustment is required
• relying on one thickness for every installation
• improvising with timber, cardboard, or offcuts
• failing to keep enough stock in the van

The correct width and thickness should always be chosen based on the actual support requirement.

Who Should Buy 20mm Glazing Packers?

20mm flat glazing packers are useful for:

• window installers
• door installers
• glazing companies
• maintenance teams
• conservatory installers
• builders
• contractors
• trade buyers managing van stock

They are especially useful for installers who regularly encounter narrower systems or compact support points.

Buying 20mm Glazing Packers in Bulk

For trade buyers, 20mm glazing packers are best bought in packs of 1000 because they are consumable products used repeatedly across jobs.

Bulk buying helps installers:

• keep stock available
• reduce reordering frequency
• avoid site delays
• standardise van stock
• reduce emergency purchases
• keep the right thicknesses ready

If you use 20mm packers regularly, it makes sense to keep the main working thicknesses in bulk rather than ordering only when stock runs out.

Recommended 20mm Stock Setup

For most installers, a sensible 20mm flat glazing packer setup would be:

• 3mm as the main everyday thickness
• 5mm for heavier support and larger gaps
• 1mm and 2mm for fine adjustment and lighter corrections

If you work across multiple glazing systems, it is also worth stocking 24mm and 28mm flat glazing packers alongside 20mm so you can choose the correct width for each job.

Final Thoughts

Installers should use 20mm flat glazing packers when the job calls for a narrower flat packer, compact support, or accurate spacing in a 20mm glazing system.

They are especially useful for standard window and door glazing where a wider packer is not required. For trade buyers, the most useful 20mm thicknesses are usually 3mm for everyday support and 5mm for stronger correction, with 1mm and 2mm kept for fine adjustment.

Explore our 20mm flat glazing packers in packs of 1000 and choose the thicknesses that match your installation work.