6 mil vs 10 mil vs Heavier Liners
Our Top Pick
A 10-mil polyethylene liner is the right choice for most crawl spaces — thick enough to survive the install and occasional access, and stocked on Amazon in 10 ft and 12 ft widths. If your crawl space is used for storage, gets walked on regularly, or your inspector specifies a Class A (ASTM E1745) retarder, buy a 15–20 mil liner from an insulation supplier instead.
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Quick answer
A 10-mil polyethylene liner is the right crawl space vapor barrier for most homes, and the Crawldryer 10 × 100 ft roll is where to start. Mil thickness is the specification that matters: 6-mil meets many codes but tears during installation and on every future crawl, while 10 mil survives being laid down and entered occasionally. Rule of thumb — if anyone will be in that crawl space regularly, or an inspector has specified an ASTM E1745 Class A retarder, skip the retail rolls and order a 15–20 mil reinforced liner from an insulation supplier.
Every pick below is currently stocked — ratings and stock read from Amazon on 20 September 2026.
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 20 Sep 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
Listing verified 20 Sep 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
Amazon price verified 17 Aug 2026
Reviewed by Marcus ReedIICRC Certified WRT
Updated September 20, 2026 · Independent expert review — no sponsored placement
Before you buy
Equipment earns its money against damp air and finished drying. Standing water, soaked drywall or carpet, a leak that keeps coming back, or a musty smell that survives cleaning are past what any consumer unit removes — those need source-fixing and measured structural drying. One call tells you which side of that line you're on, with costs explained before anything is agreed.
Pros in this network carry
Each pick is scored on three dimensions by Marcus Reed, our IICRC-certified Water Restoration Technician, against the drying targets in IICRC S500 — the standard restoration crews work to. Capacity, airflow and power draw come from the manufacturer's published figures; reliability and ease of use are weighed from verified-buyer reports on the current listing. Ratings, review counts and stock on this page are read from Amazon and carry the date they were read.
Value
Price against capacity and build — does the unit justify its cost on a typical water damage job?
Performance
Rated moisture removal and airflow against IICRC S500 drying targets, plus what buyers report over long runs.
Ease of Use
Setup time, control clarity, portability, and how easily a non-professional can operate it.
Full Reviews
Scores out of 10, weighted for how the unit is used on a real water-damage job.
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Listing verified 20 Sep 2026
Quick Verdict
The sensible default for a dirt crawl space — 10-mil polyethylene, 1,000 sq ft to a roll, thick enough to install without tearing.
Score Breakdown
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
Expert Note
Marcus Reed · IICRC Certified WRT · 15 yrs experience
“10 mil is the practical floor for a crawl space you intend to leave alone. The failure I see over and over 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, buy a 15–20 mil reinforced liner from an insulation supplier — that class of product is not sold on Amazon. 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: IICRC S500 practice is 12-inch overlaps sealed with vapor barrier tape, not loose overlaps.”
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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 20 Sep 2026
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.
Score Breakdown
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
Expert Note
Marcus Reed · IICRC Certified WRT · 15 yrs experience
“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 liner from an insulation supplier.”
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$39
Amazon price verified 17 Aug 2026
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.
Score Breakdown
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
Expert Note
Marcus Reed · IICRC Certified WRT · 15 yrs experience
“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. The 6-mil sheets I pull out are 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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What to know before you buy — written from real restoration job experience.
Vapor barrier thickness is measured in mils (thousandths of an inch). The IRC sets 6 mil as the minimum ground cover for a crawl space, but moisture control professionals 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, and it is the heaviest thickness reliably stocked on Amazon. Above that, 15–20 mil reinforced liners exist for crawl spaces that get used, and they are ordered through insulation and building-supply houses rather than bought online.
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 reinforced 15–20 mil sheet 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. Third, a full conditioned encapsulation, where the liner is relied on as part of the building envelope. In all three cases, call an insulation supplier and ask for a Class A crawl space liner — that product class is not an Amazon purchase.
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-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 entirely on seam integrity. IICRC S500 practice is 12-inch overlaps at all seams, sealed with vapor barrier tape — not duct tape, which fails in humid conditions. Run the barrier 6 inches up foundation walls and seal with compatible tape or hydraulic cement. Any unsealed gap — around pipes, posts, or wall transitions — defeats the purpose of the barrier. This is also why roll width matters: a wider sheet means fewer seams, and fewer seams means fewer places to fail. Most DIY vapor barriers fail at the seams, not 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.
How HearthDry evaluates equipment
Every product on this page has been evaluated by Marcus Reed, a 15-year IICRC Water Restoration Technician (WRT) who has worked on hundreds of residential and commercial water damage jobs. Products are scored across three weighted dimensions: Value, Performance, and Ease of Use.
Test Conditions
HearthDry maintains editorial independence. Affiliate commissions do not influence rankings — the top pick is the product we would buy for most homeowners, not the highest-commission product. Prices are verified monthly and updated when they shift more than 10%.
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, and it is the heaviest liner reliably stocked on Amazon.
Go heavier — 15 to 20 mil reinforced — if the crawl space is walked on regularly, used for storage, or if an inspector or engineer has specified an ASTM E1745 Class A retarder. Those heavier liners are ordered through insulation and building suppliers rather than bought online.
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.
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