# Best Vapor Barrier for a Crawl Space: How to Choose

> Which crawl space vapor barrier to choose — reinforced vs unreinforced, mil ratings, ASTM E1745 and what actually matters in a space people crawl through.

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# How to Choose the Best Vapor Barrier for a Crawl Space

Decision guide How to Choose the Best Vapor Barrier for a Crawl Space Reinforcement matters more than thickness. Updated 2 August 2026 The best crawl space vapor barrier is a reinforced liner of 12–20 mil meeting ASTM E1745, with a permeance below 0.1 perms. Reinforcement matters more than the mil number: reinforced 12 mil outlasts unreinforced 20 mil in any crawl space someone actually enters.

## Reinforced vs unreinforced

Reinforced liner has a scrim layer — a woven mesh — sandwiched between plies of polyethylene. That mesh is what stops a puncture becoming a tear that runs the length of the sheet. Unreinforced sheet of the same thickness punctures and then splits. This is why comparing products on mil rating alone gets people the wrong material: the construction matters more than the number.

## What ASTM E1745 guarantees

ASTM E1745 sets minimums across water vapor permeance, tensile strength and puncture resistance. A product either meets it or it does not, and it is the only meaningful shorthand for whether a liner is fit for the job. A Class I vapor retarder is one at 0.1 perms or below. That is the property doing the actual work of stopping soil moisture entering as vapour.

## Which thickness for which situation

12 mil reinforced is appropriate for most crawl spaces that see occasional service access. 20 mil is worth it where the space is entered regularly, where there is equipment down there needing maintenance, or where the ground is rough and sharp. Occasional access, smooth ground — reinforced 12 mil Regular access or equipment servicing — reinforced 16–20 mil Storage use — 20 mil, and consider a walkway layer Any thickness unreinforced — not suitable

## The bottom line

Ask two questions of any quote: is the liner reinforced, and does it meet ASTM E1745. If the answer to either is unclear, the mil number on its own tells you very little. For a number against your own crawl space, use the cost estimator , or call (910) 886-2018 and we will come and measure it. Get an exact quote A free on-site measure beats any online range. Website What do you need? Select a service… Crawl Space Encapsulation Crawl Space Insulation Crawl Space Waterproofing Crawl Space Mold Removal Crawl Space Vapor Barrier Installation Crawl Space Dehumidifier Installation Crawl Space Drainage Crawl Space Sump Pump Installation Crawl Space French Drain Crawl Space Cleanup Crawl Space Structural Repair Sagging Floor Repair Crawl Space Door Replacement Flood Vent Installation Not sure — I need someone to look ZIP code Continue Your name Phone What are you seeing? (optional) Back Request my inspection Got it — your request is in. We'll be in touch with a quote. Related service Crawl Space Vapor Barrier Installation Related guides What Thickness Vapor Barrier Does a Crawl Space Need? Vapor Barrier for a Crawl Space: Spec and Standards Crawl Space Encapsulation vs. Vapor Barrier Is Crawl Space Encapsulation Worth It? DIY Crawl Space Encapsulation All guides → , not a heading: this is a CTA, not a section of the document outline. --> Get your crawl space measured and priced Free on-site inspection across Wilmington and New Hanover, Brunswick and Pender counties. Free quotes within 24 hours. Call (910) 886-2018 Get a free quote

## Questions

Is 6 mil plastic OK for a crawl space? No. 6 mil unreinforced builder sheet fails both the puncture resistance and tensile requirements for crawl space service, and tears the first time anyone crawls on it. Is thicker vapor barrier always better? Not if it is unreinforced. Reinforced 12 mil will outperform unreinforced 20 mil in service. Reinforcement first, then thickness. What is the difference between a vapor barrier and a vapor retarder? In practice they are used interchangeably for crawl space liner. Technically a Class I vapor retarder is 0.1 perms or below, which is the specification that matters.