Plastic sheeting stamped 6 mil is 0.006 inch (0.15 mm) thick — a common construction-grade film for moisture and vapor control.
One number on a plastic roll tells you exactly how much punishment it can take, if you know what the unit means. The “6” on 6 mil plastic sheeting is a thickness rating, not a quality score, and reading it wrong is how thin covers end up stretched over wet crawl spaces.
This article explains the rating in inches and millimeters, what 6 mil film is actually built for, and where it runs out of strength.
How Thick Is 6 Mil Sheeting, Really?
Plastic sheeting rated 6 mil is 0.006 inch thick — six one-thousandths of an inch, or 6/1000 inch. The name comes from mille, Latin for “thousand,” and the math stays honest: on film labels, mil always means one-thousandth of an inch, and larger numbers mean thicker, tougher film.
The unit fools people because “mil” looks like shorthand for millimeter. It isn’t. One mil equals 0.0254 mm, so 6 mil works out to 0.1524 mm, usually rounded to 0.15 mm. A single millimeter is roughly 39 mils, so a sheet labeled 6 mm would be nearly a quarter of an inch thick — a rigid slab, not a flexible roll.
The chart below shows how common ratings translate.
| Sheeting Rating | Thickness In Inches | Thickness In Millimeters |
|---|---|---|
| 1 mil | 0.001 inch | 0.0254 mm |
| 2 mil | 0.002 inch | 0.0508 mm |
| 3 mil | 0.003 inch | 0.0762 mm |
| 4 mil | 0.004 inch | 0.1016 mm |
| 6 mil | 0.006 inch | 0.1524 mm |
| 10 mil | 0.010 inch | 0.2540 mm |
| 20 mil | 0.020 inch | 0.5080 mm |
Each step up adds one thousandth of an inch, so 6 mil is exactly twice the thickness of 3 mil film. If a supplier lists the same sheet as 0.15 mm, it is the same 6 mil product in metric clothing. Global Plastic Sheeting’s mil thickness chart covers the full range of ratings if you need values beyond these.
What 6 Mil Sheeting Is Built For
Six mil is the default general-purpose thickness for jobs that need a genuine moisture or debris barrier without paying for the heaviest film. It hits the balance point: thick enough to shrug off normal jobsite abuse, cheap enough to dispose of when the work is done. Builders and homeowners reach for it in the same situations:
- Vapor barriers and vapor retarders under slabs, in crawl spaces, and over dirt floors
- Temporary covers for building materials, equipment, and openings
- Construction enclosures and remediation covers
- Greenhouse covers and painting protection
- General waterproofing and moisture control in damp, tight spaces
In all of these roles the film is genuinely waterproof: water beads on the surface instead of soaking through, which is exactly what a vapor barrier must do. Four-mil film handles dust and light spatter, but 6 mil is the step up that most people choose once water is involved.
When you’re ready to buy, we’ve already compared the best 6 mil plastic sheeting options on price, strength, and roll size.
Where 6 Mil Falls Short
The rating tells you thickness, not toughness: 6 mil is durable for general-purpose work but sits on the thin end of the heavy-duty range. Plain 6 mil punctures more easily than 10 mil or 20 mil products when it is dragged over sharp gravel or rough concrete.
Reinforced sheeting changes that math. A scrim or grid layer can make a nominally 6 mil product tougher than plain film with the same rating, and reinforced sheet is measured at the cross-section of the internal grid rather than at the film face. That is why two rolls both stamped 6 mil can feel very different in hand.
If you want certainty about what you are holding, a digital thickness gauge or micrometer measures the actual film in seconds. Building codes frequently cite 6 mil as the vapor barrier standard, but local jurisdictions differ, so verify the requirement for your area before installing.
For crawl space encapsulation, most contractors step up to 10 mil or thicker. The film gets dragged across joists, fasteners, and rocks, and thin material tears instead of sliding over them. And no rating survives the sun forever: ultraviolet light breaks down polyethylene over time, so outdoor covers should always be treated as temporary.
A ten-second micrometer check before you buy settles what the label actually means — and that habit prevents most wrong-film mistakes in the first place.
FAQs
Is 6 mil plastic sheeting the same as 6 mm?
No. A mil is one one-thousandth of an inch, while a millimeter is roughly 39 mils. Six mil works out to 0.006 inch, or about 0.15 mm, so a sheet labeled 6 mm would be nearly a quarter-inch thick and completely rigid by comparison. The two units sound alike, but they are nowhere near equal.
Can 6 mil plastic sheeting stop water?
Yes, 6 mil polyethylene sheeting blocks liquid water and is commonly used as a vapor barrier or vapor retarder for moisture control. It is the usual choice for crawl space ground covers, under-slab barriers, and temporary covers that need to stay dry. Vapor barriers also slow the movement of ground moisture, which is what makes the film effective in humid crawl spaces.
Should I use 6 mil or 10 mil for a crawl space?
Most contractors recommend 10 mil or thicker for crawl space encapsulation. Six mil works in a pinch and is a common general-purpose vapor barrier