When it comes to getting clean, level, and long-lasting results in construction, the details matter. But with different thicknesses, sizes, and colours available, a common question we hear is “which plastic packer should I use for the job?” In this quick guide, we’ll help you choose the right packer for your next project – whether you’re spacing a window frame, levelling a cabinet, or aligning floor joists.

What is a Plastic Packer?

A plastic packer (also called a shim or spacer) is a flat, durable insert used to create space, level surfaces, or provide alignment between materials. They’re often used for:

• Door and window installation
• Kitchen and bathroom fitting
• Timber framing
• Glazing systems
• Flooring and decking

They’re available in various thicknesses and colour-coded for easy identification.

How to Choose the Right Packer: What to Consider

Flat plastic shims are available in a range of sizes at BPFonline.co.uk,  including widths of 28mm, 30mm, and 32mm, and thicknesses ranging from 1mm – 6mm.

Selecting the correct size packer will rely on your project requirements:

• Gap size – Accurately measure the space between the frame and the glass.
• Frame material – Consider the type of frame being used, aluminium or wood might require a different size than UPVC frames.
• Weight – Heavier glass panes may require thicker packers to ensure proper support.

Common Glazing Packer Size Applications:

• 1mm – 2mm thickness: adjustments and levelling.
• 3mm – 4mm thickness: Standard spacing for residential windows.
• 5mm – 6mm thickness: To support heavy-duty glass.

Flat Plastic Packers Colour Codes Explained:

• Green – 1mm Thick
• Black – 2mm Thick
• White – 3mm Thick
• Grey – 4mm Thick
• Blue – 5mm Thick
• Red – 6mm Thick

Pro Tips for Using Flat Packers:

1. Double-check measurements: Always measure both the glazing unit and the aperture carefully. Small errors can lead to gaps, misalignment and poor sealing.
2. Use multiple packers to spread the load: For heavier glass units, use packers at multiple points along the base and sides to evenly distribute the weight and avoid stress points.
3. Avoid overpacking: Adding too many or too-thick packers can put pressure on the frame or glass, increasing the risk of cracking, distortion, or seal failure.
4. Ensure correct positioning: Packers should support the unit at the quarter points (roughly 1/4 in from each angle), not just the centre or corners.
5. Keep a mixed pack on hand: familiarise yourself with the plastic packer colour code and save time on site with unpredictable installs or fine-tuning.

Choosing the right packer isn’t just about size, it’s about precision, durability, and easy installations. Whether you’re a seasoned tradesperson or a DIY fanatic, plastic packers will give your project a professional finish.