Plastic flat packers in 100 x 28mm format, available in six colour-coded thicknesses from 1mm to 6mm. Sold in bags or bulk boxes. Standard size used across window fitting, door hanging, structural framing and general levelling work.
Available options and pricing for Flat Packers - Bags & Bulk Boxes, with quantity selectors and a running total
Size
QTY
SKU
Price
QTY
Total
Green - 100 x 28 x 1mm
200
P1GREEN
£3.89£4.67
—
Black - 100 x 28 x 2mm
200
P2BLACK
£3.99£4.79
—
White - 100 x 28 x 3mm
200
P3WHITE
£4.89£5.87
—
Grey - 100 x 28 x 4mm
200
P4GREY
£4.99£5.99
—
Blue - 100 x 28 x 5mm
200
P5BLUE
£5.49£6.59
—
Red - 100 x 28 x 6mm
200
P6RED
£5.99£7.19
—
100 x 28 x 1mm-6mm
1200
1200MIXPACKERS
£28.90£34.68
—
Green - 100 x 28 x 1mm
1000
P1GREENBU
£15.90£19.08
—
Black - 100 x 28 x 2mm
1000
P2BLACKBU
£16.90£20.28
—
White - 100 x 28 x 3mm
1000
P3WHITEBU
£19.92£23.90
—
Grey - 100 x 28 x 4mm
1000
P4GREYBU
£19.84£23.81
—
Blue - 100 x 28 x 5mm
1000
P5BLUEBU
£22.78£27.34
—
Red - 100 x 28 x 6mm
1000
P6REDBU
£26.90£32.28
—
Flat packers are one of those things you never think about until you run out of them mid-job. These 100 x 28mm plastic flat packers cover the standard sizes used across window and door installation, structural framing, and general levelling work. Available in six colour-coded thicknesses — 1mm through to 6mm — so you can quickly grab what you need from the bag without measuring every time. Colour coding is a small thing that saves real time on site.
Each colour corresponds to a specific thickness: green for 1mm, white for 2mm (also available as plain black), red for 3mm, grey for 4mm, blue for 5mm, and yellow for 6mm. This follows the widely used industry colour convention, which means if you have fitters from different companies working the same job, everyone’s reading from the same page.
Where Flat Packers Get Used
Window installation is the obvious one. Getting a frame plumb and level in an opening that’s rarely either requires a combination of thicknesses, and having a full range to hand stops the job turning into a guessing game with folded cardboard. Door frames, bi-fold systems, and composite door sets all benefit from the same approach.
Beyond fenestration, these turn up regularly in structural steel packing, cavity closer work, kitchen unit installation, and anywhere a subframe needs to be brought to a consistent plane before fixing. Timber frame, steel frame, it doesn’t much matter — a flat packer does the same job regardless.
Available in bags of 200 for lighter jobs or bulk boxes of 1000 and 1200 for high-volume installation work. If you’re fitting a development’s worth of windows, buying in bulk is the only sensible way to go. Running out of packers on a big frame job is the sort of thing that costs you a full hour while someone drives to a builder’s merchant.
Pro Tip: When stacking multiple flat packers to achieve a combined thickness, keep them to a maximum of three deep wherever possible — a tall, thin stack under a heavy frame can tip or compress unevenly under load.
Flat packers are used across window and door installation to level, plumb and square frames within openings. They're equally at home in structural applications where steel or timber needs to be brought to a consistent height or plane before bolting. Kitchen fitters use them under units on uneven floors, and dry lining contractors reach for them when hanging metal stud work off an out-of-true wall. Essentially, any trade that needs to close a small gap accurately without shimming with scrap timber will find a use for them.
Best For
Window frame installation
Door hanging and alignment
Structural steel packing
Kitchen unit levelling
Dry lining and stud work
Cavity closer bedding
Available In
1mm — Green
2mm — White
3mm — Red
4mm — Grey
5mm — Blue
6mm — Black or Yellow
Bags of 200
Bulk boxes of 1000 or 1200
Key Features
Colour-coded by thickness for fast site identification
100 x 28mm standard industry format
Rigid plastic construction
Stackable for combined thicknesses
Consistent dimensions throughout
Not suitable for: Not intended for load-bearing applications where compressive strength is a structural requirement. Not suitable as a permanent fixing solution on their own — always mechanically fix frames once packed.
Select the appropriate thickness or combination of thicknesses needed to bring the frame to level. Place packers beneath the frame sill or behind the jambs at fixing points, not mid-span where there is no support behind them. Use a spirit level to confirm plumb and level as you go, adjusting packer combinations until the frame sits correctly in the opening.
Once the frame is positioned, fix through or alongside the packers as required by the frame system. Do not remove packers after fixing — they remain in place to support the frame and prevent movement over time.
Measure the gap between the frame and the structural opening at each fixing point
Select the closest matching packer thickness or stack a combination to match the required gap
Place packers at fixing point locations, not between fixings where there is no backing support
Check the frame for plumb, level and square using a spirit level
Adjust packer combinations as needed until the frame sits correctly in the opening
Fix the frame in place through or alongside the packers per the manufacturer's fixing instructions
Leave packers in position permanently to maintain frame alignment
Do these follow the standard industry colour coding for packer thicknesses?
Yes, these use the standard colour convention widely adopted across the UK window and door installation industry. Each colour corresponds to a specific thickness, so they will be familiar to most fitters and can be mixed with packers from other suppliers without confusion.
Can flat packers be stacked to achieve in-between sizes?
Yes, they are designed to be stacked. A 1mm and a 2mm together give you 3mm, and so on. Keep stacks to three deep where possible — beyond that you risk the stack shifting or compressing unevenly under the weight of the frame.
What is the difference between the bag and bulk box quantities?
Bags contain 200 packers and are suited to smaller jobs or where you want a working supply of a specific thickness. Bulk boxes contain 1000 or 1200 packers depending on size and are the better option for high-volume installation work such as housing developments or commercial fit-outs.
Manufactured from rigid plastic to maintain consistent dimensions under load without deforming during installation. At 100 x 28mm these match the standard format used across UK window and door systems. Colour pigmentation is used to distinguish thickness across the range, which provides a reliable visual reference on site without requiring measurement of individual packers.
Dimensions
100 x 28mm
Thickness Range
1mm, 2mm, 3mm, 4mm, 5mm, 6mm
Colour Coding
Green 1mm, White 2mm, Red 3mm, Grey 4mm, Blue 5mm, Black/Yellow 6mm
Material
Rigid plastic
Pack Sizes
200, 1000, 1200
SKU
WGFP
Size
100 x 28 x 1mm-6mm, Black – 100 x 28 x 2mm, Blue – 100 x 28 x 5mm, Green – 100 x 28 x 1mm, Grey – 100 x 28 x 4mm, Red – 100 x 28 x 6mm, White – 100 x 28 x 3mm
Box Quantity
1000, 200, 1200
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