6 mil vs 10 mil vs 20 mil Woven, and the Tape That Seals the Seams
4 picks compared · prices, ratings and stock checked October 11, 2026
Our Top Pick
The Crawldryer 10-mil Crawl Space Vapor Barrier (10 × 100 ft) is the right liner for a crawl space you enter a few times a year. If it stores anything, gets walked on, or houses a dehumidifier you will service, step up to the Whitecap Woven 20 Mil Vapor Barrier (12 × 100 ft); if an inspector calls for an ASTM E1745 Class A retarder, order one with published test data from an insulation supplier.
4.6 on Amazon · 407 ratings
Quick answer
The best crawl space vapor barrier for most homes is the Crawldryer 10-mil Crawl Space Vapor Barrier (10 × 100 ft): if the crawl space is entered only a few times a year, buy it, because 10 mil survives installation where 6 mil tears and one roll covers 1,000 sq ft. It is rated 4.6 stars across 407 Amazon ratings. If anyone will crawl on it regularly or store things there, buy the Whitecap Woven 20 Mil Vapor Barrier (12 × 100 ft) instead. Either way, overlap seams at least 6 in., as the IRC requires in unvented crawl spaces, and seal them with vapor barrier tape, not duct tape.
Available picks first — 3 of 4 in stock at our last check — ratings and stock read from Amazon on 11 October 2026.
| Pick | Product | Rating | Where to buy |
|---|---|---|---|
| Best Overall | Crawldryer 10-mil Crawl Space Vapor Barrier (10 × 100 ft)4.6★ | 4.6★ | Check price |
| Best 20 Mil Liner (Woven) | Whitecap Woven 20 Mil Crawl Space Vapor Barrier (12 × 100 ft)4.6★ | 4.6★ | Check price |
| Best Budget | Husky 6-mil Poly Plastic Sheeting4.5★ | 4.5★ | Check price |
| Best for Wide Spans | Crawldryer 10-mil Crawl Space Vapor Barrier (12 × 100 ft)not stocked | — | Alternatives |
Best for: Homeowners lining a dirt crawl space that gets entered a few times a year — a liner heavy enough to install without shredding, in the width that fits most crawl spaces
Listing verified 5 Nov 2026
Best for: Crawl spaces used for storage, walked through to reach equipment, or lined as the first step toward full encapsulation
Listing verified 5 Nov 2026
Best for: Temporary moisture protection or very low-moisture crawl spaces where budget is the primary constraint — not recommended as a permanent encapsulation solution
10 ft × 100 ft roll · listing verified 5 Nov 2026
Best for: Wide or open crawl spaces where seam count is the problem — every taped seam is a place the barrier can fail, and a 12 ft sheet gives you fewer of them
No longer stocked — kept because the verdict still holds.
How this page was made: we compare the current Amazon listings, the makers' published specs and what verified buyers report, then rank by fit for the job. Ratings, review counts and stock are read from Amazon and dated. We earn a commission on purchases through our links; it does not change the order. Reviewed by Marcus Reed, IICRC-certified Water Restoration Technician.
Full Reviews
Each pick in detail: what the listing states, what buyers report, and where it falls short.
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on Amazon ↗
Listing verified 5 Nov 2026
See it on Amazon ↗Quick Verdict
The Crawldryer 10-mil roll is the sensible default for a dirt crawl space — polyethylene, 1,000 sq ft to a roll, thick enough to install without tearing.
Key Specs
Thickness
10 mil
Material
Low-density polyethylene
Roll Size
10 ft × 100 ft
Coverage
1,000 sq ft
Finish
Black one side, white one side
Brand
Crawldryer
Pros
Cons
Suited to
Homeowners lining a dirt crawl space that gets entered a few times a year — a liner heavy enough to install without shredding, in the width that fits most crawl spaces
Our take
10 mil is the practical floor for a crawl space you intend to leave alone. The common failure is 6-mil poly that was intact the day it went down and full of holes a year later, because someone knelt on it over a sharp rock. 10 mil takes that abuse. What it is not is a walking surface: if the crawl space stores anything, or a technician will be in there twice a year servicing a dehumidifier, step up to a 20-mil woven liner such as the Whitecap on this page. The listing says the film mitigates radon gas; no ASTM class is published for it, so do not treat it as a radon barrier. Whatever you buy, the seams decide the outcome: overlap them and seal them with vapor barrier tape rather than leaving loose laps.
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These open a search for this model. We quote prices only where we can verify them — Amazon, Sylvane and eBay.
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Listing verified 5 Nov 2026
See it on Amazon ↗Best 20 Mil Liner (Woven)
Quick Verdict
The Whitecap Woven 20 Mil is the liner for a crawl space people actually use: double the thickness of 10-mil film, woven against tears, and 12 ft wide for fewer seams.
Key Specs
Thickness
20 mil
Material
Woven (interlaced) polyethylene
Roll size
12 ft × 100 ft
Coverage
Up to 1,200 sq ft
Color
White
Weight
About 80 lb, per the listing's item data
Pros
Cons
Suited to
Crawl spaces used for storage, walked through to reach equipment, or lined as the first step toward full encapsulation
Our take
Thickness and construction answer different problems. Going from 10 to 20 mil doubles the film, and the woven construction, per the listing, resists tears and punctures better than plain sheeting, which is why reinforced liners are the type commonly specified where people will crawl. That is the case for buying this roll: a crawl space that houses a dehumidifier, a water heater or stored boxes gets visited, and every visit puts a knee on the liner. What it does not do is publish a perm rating or an ASTM E1745 class, so treat it as a tougher ground cover rather than a documented Class A retarder. Seal its seams with vapor barrier tape like any other liner.
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10 ft × 100 ft roll · listing verified 5 Nov 2026
See it on Amazon ↗Quick Verdict
Lowest cost but not a permanent liner — 6 mil punctures during installation and lets through several times the moisture vapor of an engineered retarder.
Key Specs
Thickness
6 mil
Material
Polyethylene
Water Vapor Transmission
0.06 perms
Fire Rating
None listed
Use Case
General purpose / temporary
Pros
Cons
Suited to
Temporary moisture protection or very low-moisture crawl spaces where budget is the primary constraint — not recommended as a permanent encapsulation solution
Our take
6-mil poly is what many older homes have in their crawl spaces — installed decades ago by the original builder, and it is still the code-minimum ground cover under the IRC. Code minimum and durable are different things. Old 6-mil sheets are typically perforated wherever anyone knelt on them. If you are replacing an existing 6-mil barrier, step up to at least 10 mil; the cost difference is small relative to how much longer the liner stays intact.
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Listing verified 5 Nov 2026
See it on Amazon ↗No longer stocked. We keep the review because the verdict still holds — the link opens Amazon's current results for this model and its successors.
Best for Wide Spans
Quick Verdict
The same 10-mil film in a 12 ft width — buy it to cut the number of taped seams across a wide crawl space.
Key Specs
Thickness
10 mil
Material
Low-density polyethylene
Roll Size
12 ft × 100 ft
Coverage
1,200 sq ft
Roll Weight
48.6 lb
Finish
Black one side, white one side
Pros
Cons
Suited to
Wide or open crawl spaces where seam count is the problem — every taped seam is a place the barrier can fail, and a 12 ft sheet gives you fewer of them
Our take
Pick this one on geometry, not performance — it is the same film as the 10 ft roll. Measure the short dimension of your crawl space and divide by the roll width: a 24 ft span is two clean passes of the 12 ft roll versus three of the 10 ft, which is one less seam to tape on every run. Budget a helper for the roll; at nearly 50 lb it does not go through an 18-inch hatch gracefully. And if the crawl space will be walked on regularly, the extra width does not fix that — you want a heavier woven liner, such as the Whitecap 20 mil on this page.
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What to know before you buy.
Vapor barrier thickness is measured in mils (thousandths of an inch). Six-mil polyethylene is the long-standing code-minimum ground cover, and at around 0.06 perms it already qualifies as a Class I vapor retarder (0.1 perm or less). Moisture control professionals still treat 10 mil as the practical floor, because 6-mil poly punctures during installation — a sharp rock, a nail or a knee is enough. 10 mil survives the install and the occasional access that follows. Above that, 12-, 14- and 20-mil liners are all stocked on Amazon, including woven 20-mil rolls built to resist tearing, and they earn their cost in a crawl space that gets used. What thickness cannot tell you is the vapor rating; for that you need a published perm figure or ASTM class.
Three situations call for a heavier liner than 10 mil. First, a crawl space anyone walks on regularly — storage, a service path to a dehumidifier or water heater, repeated trade visits. Foot traffic is what wears a liner through, and a 20-mil woven sheet such as the Whitecap is built for it. Second, a code or inspection requirement: some jurisdictions and most engineered encapsulation specs call for an ASTM E1745 Class A retarder, which is a tested product class, not a thickness, and none of the retail rolls on this page publish that class. Third, a full conditioned encapsulation, where the liner is relied on as part of the building envelope. A 20-mil roll from Amazon covers the first case; for the second and third, ask an insulation supplier for a liner that publishes its E1745 test data.
Perms measure how much water vapor passes through the material; lower is better. Standard 6-mil poly is commonly rated near 0.06 perms, and engineered ASTM E1745 Class A retarders publish figures an order of magnitude lower. Most retail polyethylene rolls, including the 10- and 20-mil liners here, publish no perm rating at all — so on a retail roll, thickness is the only spec you can actually verify. If a number below 0.02 perms matters to you, on paper or to an inspector, you need a product that publishes its ASTM test data, which means buying through a supplier.
Vapor barrier effectiveness depends on seam integrity. In an unvented crawl space, the IRC calls for seams overlapped at least 6 inches and sealed or taped, with the edges run at least 6 inches up the stem wall and sealed to it; many installers overlap 12 inches for margin. Use purpose-made vapor barrier tape rather than duct tape, which lets go in damp air. The seam tapes stocked on Amazon are polyethylene tapes, typically about 9 mil thick and 4 inches wide, with a rubber-based pressure-sensitive adhesive made to bond poly to poly. Wipe both faces clean and dry before taping, and press the tape down along its full length. Any unsealed gap around pipes, piers or wall transitions defeats the barrier, which is also why roll width matters: a wider sheet means fewer seams, and most DIY barriers fail at the seams rather than in the middle of the sheet.
A vapor barrier covers only the crawl space floor, controlling ground moisture. Full encapsulation covers the floor AND walls, seals all vents, and includes a dehumidifier to control both ground moisture and humid outside air. Encapsulation runs several thousand dollars professionally installed. If your crawl space humidity exceeds 70% regularly (especially in the Southeast and Gulf Coast), encapsulation is typically worth it — it prevents the mold, wood rot, and insulation damage that cost far more. Encapsulation is also the job where a heavier Class A liner is worth specifying, since the liner becomes part of the conditioned envelope.
A ground cover is the wrong first step in four situations. If water stands in the crawl space after rain, the soil has a drainage problem; gutters, grading, a perimeter drain or a sump pump come first, or the liner traps water beneath it. If a pipe or drain is leaking above the soil, fix it and dry the area, ideally within 24 to 48 hours as EPA advises for wet materials. If mold is already growing on joists or subfloor, a liner will not remove it, and EPA guidance treats more than about 10 square feet as a job that may need a professional. And if the crawl space air stays damp because humid outdoor air pours in through the vents, a floor liner alone will not fix it; that space needs sealing and dehumidification, which is where a crawl space dehumidifier comes in.
For most crawl spaces, 10 mil is the thickness to buy. 6-mil poly is the code-minimum ground cover in many areas but punctures easily during installation and any future access — one crawl over a sharp rock and it is holed. 10 mil survives the install and occasional entry.
Go to 20 mil, ideally a woven or reinforced liner, if the crawl space is walked on regularly or used for storage. If an inspector or engineer has specified an ASTM E1745 Class A retarder, buy a product that publishes that test data, which usually means an insulation supplier.
NoClass A refers to ASTM E1745, a tested product class covering water vapor transmission, tensile strength, and puncture resistance — not a thickness.
A retail 10-mil polyethylene roll can be a perfectly good crawl space ground cover while publishing no ASTM class and no perm rating at all. If your plans, your inspector, or your contractor call for a Class A retarder, a 10-mil roll will not satisfy that, however it performs in the ground. Buy a product that publishes its E1745 test data, and expect to order it from an insulation supplier.
A vapor barrier covers only the ground (dirt floor). Crawl space encapsulation covers the ground AND the walls, seals all vents, and typically includes a dehumidifier and sump pump. Encapsulation costs several times what a ground cover does, but it controls humidity more completely and can qualify the crawl space as conditioned space.
A basic vapor barrier controls ground moisture but not the humid outside air entering through the vents. If your crawl space humidity exceeds 70% regularly (especially in humid climates), encapsulation is typically worth the investment.
If the floor is bare soil, almost certainly. Soil gives off water vapor continuously, even when it looks dry, and in a crawl space that vapor ends up in the floor framing, the insulation and the air that rises into the house.
The International Residential Code calls for a continuous vapor retarder over exposed earth in an unvented crawl space. Musty smells upstairs, condensation on ducts or pipes, and damp or sagging insulation are signs the crawl space already has a moisture problem that a ground cover would help.
On a two-tone panda film like the Crawldryer liners, white faces up and black faces the dirt. The white side brightens the space for anyone working in it, and the black side stops light from reaching the soil.
The listing says both faces block water vapor, so laying it upside down does not stop the barrier working; it only leaves the crawl space darker to work in. A single-color roll such as the black Husky sheeting has no up side at all.
Not over standing water or mud. A liner laid on a wet floor traps the water underneath, where it keeps feeding humidity through every seam and gap, and the crawl space stays damp. Find the source first: a plumbing leak, gutters and downspouts emptying against the foundation, or ground that slopes toward the house.
Fix that, let the soil dry, and clear out wet debris and fallen insulation. If water comes in every time it rains, the crawl space needs drainage, and possibly a sump pump, before it needs a liner.
YesIf anyone will be in the crawl space regularly; no, if it is sealed up and left alone.
A 20-mil liner, especially a woven one, resists the punctures and tears that foot traffic, stored boxes and service visits cause, so it pays off under a dehumidifier, a water heater or a storage area. In a crawl space entered once or twice a year, 10 mil does the moisture job for less money. Extra thickness is not a vapor rating on its own, so check for a published perm figure if that matters to you.
Use a purpose-made vapor barrier seam tape: a white or clear polyethylene tape, usually about 4 inches wide and around 9 mil thick, with an aggressive rubber-based adhesive made to bond poly to poly.
It holds in a damp crawl space where duct tape and packing tape tend to peel away. Tape every overlap along its full length after wiping the film clean and dry, and use the same tape, or a compatible sealant, where the liner meets the foundation wall and wraps around piers.
At least 6 inches, and further if you are encapsulating. The IRC requires the vapor retarder in an unvented crawl space to extend at least 6 inches up the stem wall and be attached and sealed to it.
Full encapsulation carries the liner most of the way up the foundation wall, often stopping a few inches below the sill plate, which leaves a strip of wall visible for termite inspection. Fasten the top edge mechanically and seal it with tape or a compatible sealant so it cannot slip down.
Call (888) 840-6512. The line is answered 24 hours a day, seven days a week, and connects you with an IICRC-certified water damage restoration company that serves your area. A recorded menu picks up first: choose water damage or mold, key in your 5-digit ZIP code, and hold through the short silence while the call is passed to the company.
Describe what you can see — where the water is coming from, how long it has been there, and whether it smells — the more specific you are, the faster the right company is on the line. If the source is a pipe or an appliance, shut the main water valve first. Have four things ready and the call goes quickly: the address, when the water started, what is wet now, and whether you have filed an insurance claim.
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