Cavity drain membrane buying guide: stud and weight
Updated: 21 October 2026
You are looking at amazon.co.uk because a wall, a foundation or a cellar floor needs a sheet, and the word membrane is doing too much work. A cavity drain membrane buying guide has to separate a studded HDPE roll from weed fabric and from flat polythene before you compare prices. A named certificate still does not mean the sheet holds back water pressure. The four listings in the [dimpled membrane comparison](/hub/flooring/dimpled-membrane) are the set used here: two Einside rolls with a printed area, and two generic panels whose widths do not agree. A purchase through our links can earn a commission at no extra cost to you.
You are looking at amazon.co.uk because a wall, a foundation or a cellar floor needs a sheet, and the word membrane is doing too much work.
You are looking at amazon.co.uk because a wall, a foundation or a cellar floor needs a sheet, and the word membrane is doing too much work. A cavity drain membrane buying guide has to separate a studded HDPE roll from weed fabric and from flat polythene before you compare prices. A named certificate still does not mean the sheet holds back water pressure. The four listings in the dimpled membrane comparison are the set used here: two Einside rolls with a printed area, and two generic panels whose widths do not agree. A purchase through our links can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Stud height | Weight per m² | Coverage | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Einside Einside embossed HDPE membrane, 2 m × 20 m | 8 mm | 400 g/m² | 40 m² | 8.8 | about £69.50 | View offer |
| Alternative |  Einside Einside embossed HDPE membrane, 1 m × 20 m | 8 mm | 400 g/m² | 20 m² | 8.0 | about £50.00 | View offer |
 Generic Generic holed dimpled drainage panel, £146.98 | Not stated | 700 g/m² (bullet) | Not settled | 4.0 | about £146.98 | View offer |
On this page
What you are actually buying
Four products answer a search for membrane. A dimpled sheet is studded high-density polyethylene. The studs keep a void so moisture can move in the gap instead of sitting against the finish. A flat damp-proof membrane is continuous polythene. In England, Approved Document C’s example for a ground-bearing floor that is not under water pressure is polyethylene of at least 300 µm (1,200 gauge), with sealed joints. Weed-control fabric is woven polypropylene and does not form a cavity. The polythene split is on the damp-proof membrane page. A smooth clear sheet or a woven mat is a different job.
Stud height and weight
Newton’s CDM range includes 3 mm, 8 mm and 20 mm sheets. CDM 508 is an 8 mm membrane at 500 g/m² or 700 g/m², with the heavier grade used on floors under BBA 22/6357. PUDLO quotes about 4 litres per square metre for an 8 mm sheet and about 14 litres for a 20 mm sheet. An air-gap figure such as 14.61 litres on Wykamol CM20 is not a drainage-capacity line, so do not set it beside a listing that says about 4.6 litres per square metre. The Einside rolls state 8 mm, 400 g/m² and about 4.6 litres per square metre: 40 m² at £69.50, and 20 m² at £50.00. If the detail names 700 g/m², the 400 g/m² sheet is the wrong product.
Mesh, geotextile and the rest of the basket
A plain stud gives you the gap, not a key for plaster or dot-and-dab. A mesh face is a different product. A geotextile is the filter cloth where soil would wash fines into the studs. The Einside listings state neither. The £146.98 panel tells you to use a geotextile and does not include one. Plugs, tape and a drain are separate on every listing here. Add brick plugs and tape to the £69.50 roll and the basket is no longer the headline price. The fixing sequence is on how to fit cavity drain membrane.
What a certificate does not say
A BBA certificate means a named system was assessed. It does not make the sheet a barrier against standing water. Wykamol, Sika and Newton CDM 508 wording says the membrane, as installed, is not resistant to hydrostatic pressure. The cavity is for seepage. The structure remains the primary resistance. PCA’s Type C guidance from June 2022 puts a first service within three months, then at least yearly. None of these four listings names a certificate. F-DM 15/03/05 is not a BBA number. If the room must be habitable, leave these rolls. Grades and pumps are on the basement page.
How to read a contradictory listing
One generic panel costs £106.99. The title states 0.5 m by 25 m and also 30 cm by 25 m, while a bullet states 0.5 m by 25 m and 700 g/m². The £146.98 title adds 70 cm by 25 m beside the same 0.5 m bullet. Both technical blocks say 1 kg and a package of 8 by 8 by 8 cm. A 25 m sheet at 700 g/m² cannot also be a 1 kg cube, so you cannot quote a price per square metre against about £1.74. When the title and the bullet disagree on width, leave the listing.
Common questions
Is 8 mm the stud I should buy by default?
Eight millimetres is the stud height printed on both Einside rolls, and it is the height Newton uses on CDM 508. It is not a universal default. A floor detail that names 700 g/m², or a design that specifies a 20 mm void such as PUDLO CD20, is asking for a different sheet. Match the stud and the grams to the drawing before you match the price.
What does grams per square metre tell you?
It is the mass of the plastic, not a waterproofing grade by itself. The Einside pages state 400 g/m². Newton’s 8 mm trade sheet is described at 500 g/m² or 700 g/m², with the heavier one used on floors. A higher number on a generic bullet is only useful if the width, the weight of the parcel and the dimple height agree, which they do not on the two unrated panels.
Do you need a mesh face?
You need a mesh face if the finish is plaster or dot-and-dab that has to key to the membrane. A plain stud does not provide that key. The Einside listings do not state a mesh. If you are only protecting a foundation before backfill, the mesh is a different requirement, and the reviews that exist describe that external job rather than an internal finish.
Does a BBA certificate mean the roll holds water pressure?
No. The BBA sheets cited for Wykamol, Sika and Newton CDM 508 say the installed membrane is not resistant to hydrostatic pressure. The cavity manages seepage. The wall or floor structure is still the primary resistance, and the system needs a way for water to leave. None of the four listings in this set names a certificate at all.
Are the holed generic panels the same as a basement sheet?
They are described as holed dimpled drainage sheets for gardens and roofs, and the pages also name basements. They do not state a stud height, they have no star line, and the width in the title conflicts with the bullet. Until one width is confirmed, they are not a substitute for an 8 mm roll with a printed area.
What else has to go in the basket?
On these listings, plugs, tape and a drain are not in the box. A geotextile, where a bullet mentions one, is a separate layer. Budget for the plug maker’s fixings and for joint tape before you treat £50.00 or £69.50 as the cost of a finished wall.
Related pages
Sources
Public UK sources used for this comparison. Listing prices, stars and review counts are the amazon.co.uk lines kept with these four products.
- PCA Type C guidance, June 2022 (retrieved October 2026)
- Newton BS 8102:2022 technical paper (retrieved October 2026)
- Approved Document C, GOV.UK (retrieved October 2026)
- Newton CDM 508 and BBA 22/6357 (retrieved October 2026)
- Wykamol CM20 BBA sheet (retrieved October 2026)
- Newton on a DPM versus waterproofing (retrieved October 2026)
- Newton HydroBond 410 GeoDrain (retrieved October 2026)
- ABG Roofdrain (retrieved October 2026)