Plastic packers or wooden shims
Updated: 23 October 2026
You are looking at a bag of kiln-dried wood wedges and a bag of plastic glazing packers, and the wood has far more stars. The decision is where the piece will live after you stop looking at it. Leave a rot-proof packer in a closed or wet gap. Keep kiln-dried wood for a dry job you can still see and replace. Prices and review counts below are from the amazon.co.uk listings in the [shims comparison](/hub/diy-supplies/shims). A qualifying purchase can earn a commission at no extra cost to you. This was not a laboratory test of either material. The listings were read on 22 October 2026.
You are looking at a bag of kiln-dried wood wedges and a bag of plastic glazing packers, and the wood has far more stars. The decision is where the piece will live after you stop looking at it.
You are looking at a bag of kiln-dried wood wedges and a bag of plastic glazing packers, and the wood has far more stars. The decision is where the piece will live after you stop looking at it. Leave a rot-proof packer in a closed or wet gap. Keep kiln-dried wood for a dry job you can still see and replace. Prices and review counts below are from the amazon.co.uk listings in the shims comparison. A qualifying purchase can earn a commission at no extra cost to you. This was not a laboratory test of either material. The listings were read on 22 October 2026.
Our top picks
| Badge | Product | Material | Where it belongs | Piece size | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Nelson Wood Shims Nelson Wood Shims 8 in, 24 kiln-dried wedges | Kiln-dried wood | Dry, and still visible | 8 in long | 6.8 | about £9.99 | View offer |
 EVOGES EVOGES flat glazing packers, 42 mixed | Plastic | Sealed or wet gap | 28 × 100 mm | 8.8 | about £6.99 | View offer | |
| Alternative |  Onspeshow Onspeshow composite shims, 12 pack | Composite | Outdoor claim, no reviews | 8 × 1.5 in | 2.6 | about £14.99 | View offer |
On this page
What happens when the shim gets wet
Timber moves. PackersDirect lists the wood advantages as easy trimming and a natural material, and the disadvantages as moisture, rot and insects. That page is a shop argument, not a British Standard. Metal Parts Direct says timber swells and can rot, then argues for stainless steel. Use that only as a warning about timber. Stainless steel is not in this comparison.
Glazpart says setting blocks should be non-absorbent and rot-proof, and compatible with the edge seal. A kiln-dried wedge fails that the moment it stays in an external cavity. Approved Document 7 requires suitable materials. That is a duty on the work, not a badge for either bag. If the reveal will be sealed or rained on, plastic keeps the thickness you fitted.
When wood is the right piece
Wood earns its place when you want to carve a taper and you will still be able to see it. The Nelson listing, ASIN B07C38PL2N, is 24 kiln-dried wood shims, 8 inches long, at about £9.99, with the country of origin given as the USA. You can score and snap the spare end, under a skirting or a wardrobe plinth. One of three saved UK texts levelled an IKEA Pax wardrobe. A swollen shim there shows as a fresh rock, not a bowed window.
The listing asks whether the pieces are hardwood, and whether you can paint them, and answers neither. Do not call them cedar. Under a bath, on a patio bearer, or behind an external door frame, the same wedge is the wrong piece.
When plastic or composite stays in the gap
Polypropylene flats and horseshoes are the pieces to leave in a window, a door, a bathroom or an outside gap. The thickness is moulded, not carved. In this set that means the EVOGES and HuangXinyu flats at 100 × 28 mm, and the EETU horseshoes at 55 × 43 mm. You can stack two known thicknesses. You cannot whittle a plastic flat into a custom slope as easily as a wood shim.
Composite is a third column, not a second kind of wood. Onspeshow, ASIN B0H99WCTC3, is 12 scored wedges, 8 × 1.5 inches, at about £14.99. The bullets say recycled composite, a hand snap, and outdoor use without rot or swell. There is no star line, no review text, and no answered weight question. Treat the no-rot line as a seller claim. Do not use that taper as a 28 mm setting block under glass.
Stars are not a material test
Nelson's 4.7 from 2,418 reviews will beat a flat pack sorted by review count. The EVOGES flats are 4.7 from 347 at about £6.99. Only three of 47 saved Nelson texts are headed United Kingdom. The 347 include a window, a shed and decking. That is not a load test. It is the more relevant file if the gap is a frame.
A plastic pack with no reviews is not better than wood because a bullet says waterproof. For a sealed gap, choose a rigid plastic packer you can read. For a dry wardrobe, the 8 inch wedge matches the UK review you have. A rocking leg is a third path, on wedges for wobbly furniture.
Common questions
Will wooden shims rot behind a window?
They can. Timber swells and can rot when it stays damp, which is why Glazpart wants setting blocks that are non-absorbent and rot-proof. A kiln-dried wedge is dry when you buy it. It does not stay that way in an external reveal or under a bath. If you will seal the gap, use a plastic packer. If you can see the shim and the room stays dry, wood remains a fair taper.
Can I use plastic packers indoors on timber?
Yes, when you want a stable thickness more than a piece you can carve. A 100 × 28 mm polypropylene flat will pack a dry stud or a lining, and a horseshoe is the one if a screw is already there. Wood is better only when you need to trim a slope and you can still replace it. Plastic is not outdoor-only because it also survives rain.
Are the Nelson shims hardwood, and can they be painted?
The listing asks both questions and does not answer them. The material line says wood, kiln dried, not a named hardwood and not cedar. Paint is not confirmed. What is confirmed is 24 pieces, 8 inches, about £9.99, origin USA, and 4.7 from 2,418 reviews, with a UK note about an IKEA Pax wardrobe. Judge the bag on that.
Is a composite wedge the same as a glazing packer?
No. The Onspeshow pieces are 8 inch scored tapers at about £14.99, with a waterproof claim and no reviews. A glazing packer in this set is a flat of one thickness, about 100 × 28 mm, in 1 mm steps. You can snap a composite tail. You should not use that taper as a setting block under glass.
Should I leave wood under a bath or a patio bearer?
No. Those places get wet, and you will not see the shim swell. Use a non-absorbent plastic packer, or a composite taper only if you accept that the outdoor claim is unreviewed. The Nelson UK note is a wardrobe, a dry indoor base. A patio bearer is closer to the damp failure the sellers warn about.
Do I need stainless steel instead of plastic?
Only if a fitter's specification for an external frame asks for steel. A steel-shim seller recommends it and mentions creep in plastic. That is their argument, not a test of these amazon packs, and steel is not in this set. For ordinary domestic packing, polypropylene flats and horseshoes are the rot-proof choice against wood.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Scores dated 22 October 2026. Updated 23 October 2026.
- BPF Online — How to choose the right plastic packer (retrieved 22 October 2026)
- Fixfast — Plastic packing shims data sheet (retrieved 22 October 2026)
- Glazpart — Glazing accessories (retrieved 22 October 2026)
- NBS — BS 6262-1:2017 (retrieved 22 October 2026)
- Fix Direct — how glazing packers are used (retrieved 22 October 2026)
- SAJE — How to toe and heel (retrieved 22 October 2026)
- Wickes — fixing distances (retrieved 22 October 2026)
- NHBC — Section 5, first fix operations (retrieved 22 October 2026)
- Approved Document 7 (retrieved 22 October 2026)