What Does Mil Mean in Plastic Sheeting? 8 Mil Thickness Explained

A mil is 0.001 inch, so 8 mil plastic sheeting is 0.008 inch thick — roughly 0.2 mm, not 8 millimeters.

“8 mil” tells you only film thickness — not width, length, or jobsite durability. It’s constantly misread as millimeters, leaving buyers with far thinner material than expected. Here’s what the number means, where 8 mil sits on the durability scale, and which specs matter more.

How Thick Is 8 Mil Compared To A Millimeter?

8 mil equals 0.008 inch — about 0.2032 mm, roughly a quarter the thickness of an 8 mm sheet (0.315 inch). “Mil” is not short for millimeter; the units sit on different scales. A mil is one-thousandth of an inch, so 8 mil is about as thick as a heavy business card, while an 8 mm sheet is closer to a stack of 30 of those cards.

• 1 mil = 0.001 inch = about 0.0254 mm
• 8 mil = 0.008 inch = about 0.2032 mm
• 8 mm = about 0.315 inch — roughly 39 mil

What Can You Do With 8 Mil Plastic Sheeting?

8-mil film falls into the heavy-duty category, where flexibility and puncture resistance both matter. Standard polyethylene sheeting is sold in 6, 8, 10, 12, 16, and 18 mil, with 8 mil near the entry point of that band. Common uses include dust barriers and temporary enclosures, vapor barriers and crawl-space encapsulation, concrete-curing covers, landscaping and weed-control covers, furniture, equipment, and floor protection, and agricultural and transport covers.

These are reference figures for standard sheeting, not a promise every 8-mil product performs the same.

What Thickness Actually Changes (And What It Doesn’t)

Thickness predictably improves impact strength and slows vapor movement, but it does not by itself certify a sheet as a vapor barrier or make it flame-resistant. Reference data shows dart impact climbing from 40 grams at 1 mil to 370 grams at 8 mil, and permeance falling from 0.50 to 0.096.

Material matters too: an 8-mil vinyl sheet and an 8-mil polyethylene sheet can differ sharply in flexibility, tear behavior, chemical compatibility, and outdoor life. Polyethylene brings weatherability and chemical inertness; vinyl behaves differently at the same nominal gauge. Product data commonly references ASTM D4397, ASTM C171, ASTM D4635, and Federal Specifications LP-378, LP-390, and LP-512 — compare those test methods, not the mil number alone. Additives matter as well: fire-retardant, anti-static, or antimicrobial treatments each change what a product suits. “8 mil” alone never establishes fire rating, UV service life, chemical resistance, or vapor-barrier compliance.

Check individual manufacturer sheets for tolerance and test method where exact performance matters — nominal thickness is not guaranteed uniform across a roll. For side-by-side comparisons of specific rolls, this roundup of tested 8 mil plastic sheeting options breaks down the real-world differences.

How Do You Pick The Right Roll?

Match the sheet to the job first, read the technical data second, and check the mil number last. A thicker sheet is not automatically a certified vapor barrier — confirm permeance and applicable building-code requirements instead.

1. Identify the material: polyethylene, vinyl, or another polymer.
2. Confirm both nominal thickness and roll dimensions.
3. Name the job: temporary cover, crawl-space encapsulation, concrete curing, agriculture, or something else.
4. Read manufacturer technical data for impact, tear, vapor transmission, UV, chemical, and temperature performance.
5. Use compatible tape, fasteners, seams, and adhesives — compatibility is product-specific.
6. Overlap and seal joints where dust or vapor control is the goal; manufacturer instructions and local building requirements set the overlap method.
7. Shield the sheet from sharp edges, abrasion, heat, flame, and wind uplift, and inspect for punctures before trusting it.

Loose film creates trip, suffocation, entanglement, and wind hazards. Keep it away from children, animals, moving machinery, electrical equipment, and ignition sources. Do not assume ordinary polyethylene or vinyl is flame-retardant, food-safe, potable-water-safe, greenhouse-rated, or safe for direct solvent contact — verify the manufacturer’s safety data before use near heat, chemicals, or structural assemblies. Reef Industries lists the full line of polyethylene sheeting and its performance data for anyone running down the material spec.