20 mil plastic represents the heavyweight division of plastic sheeting—a robust, puncture-resistant material that stands between your project and disaster. When converted to more familiar measurements, 20 mil equals 0.02 inches or 0.508 millimeters, roughly equivalent to the thickness of 20 sheets of paper stacked together. This substantial thickness makes it the go-to choice for construction professionals, agricultural operations, and anyone who needs a barrier tough enough to withstand harsh conditions, sharp objects, and prolonged exposure.
The term “mil” itself represents one-thousandth of an inch (0.001 inch), making it distinct from millimeters or other metric measurements. Picture this: if a single human hair measures about one mil, then 20 mil plastic is as thick as 20 strands of hair side by side—transforming from delicate to durable through sheer multiplication.
What Makes 20 Mil Plastic Different
Thickness Breakdown
Understanding the actual dimensions helps grasp why 20 mil plastic performs like armor compared to its thinner cousins. Here’s how it translates across measurement systems:
| Measurement Type | 20 Mil Equivalent |
|---|---|
| Inches | 0.02 inches |
| Millimeters | 0.508 mm |
| Microns | 508 microns |
| Visual Comparison | Credit card = 30 mil |
This thickness sits at the upper end of the commercial plastic sheeting spectrum, which typically ranges from 1 mil to 100 mils for specialized applications.
Material Composition
Most 20 mil sheeting comes reinforced with a polyester string cord woven through layers of high-density polyethylene. This cross-hatched fiber mesh acts like rebar in concrete—transforming a strong material into an engineering marvel that resists tearing even when punctured. The reinforcement means a 20 mil reinforced sheet dramatically outperforms a plain 20 mil sheet without internal structure.
Primary Applications and Uses
Construction and Vapor Barriers
In construction, 20 mil vapor barriers function as the invisible shield protecting buildings from moisture invasion. These barriers excel under concrete slabs, where sharp rocks and rough aggregate would shred thinner materials. The thickness provides superior puncture resistance essential when concrete crews drag equipment and materials across the surface.
Foundation walls benefit from this thickness because it creates an impermeable membrane with extremely low permeability, blocking water vapor that would otherwise seep into walls and promote mold growth. Some specialized 20 mil barriers also restrict radon gas—a colorless, odorless radioactive gas that poses serious health risks.
Agricultural and Greenhouse Applications
Farmers and greenhouse operators choose 20 mil reinforced sheeting for projects demanding long-term durability. Applications include:
- Greenhouse covering for multi-season protection with UV resistance
- Aquaponic trough liners that withstand constant water exposure
- Pond liners for livestock or irrigation systems
- Livestock housing covers that endure high winds and heavy snow loads
The UV-stabilized versions can last 5 to 10 years outdoors, a stark contrast to construction-grade plastic that degrades within a single season.
Heavy-Duty Specialized Uses
Beyond standard construction, 20 mil sheeting serves extreme applications:
- Landfill and waste liners containing hazardous materials
- Outdoor storage covers protecting equipment year-round
- Recreational events like mud runs where crowds generate high-traffic wear
- Temporary shelters in emergency or disaster relief scenarios
Comparing Plastic Thicknesses
How 20 Mil Stacks Up Against Alternatives
Choosing the right thickness means matching material strength to project demands. Here’s the reality:
| Thickness | Strength Level | Typical Uses | Durability |
|---|---|---|---|
| 4-6 mil | Light to medium | General covers, temporary protection | Short-term (weeks to months) |
| 10 mil | Medium-heavy | Moderate construction, basic vapor barriers | 1-2 years outdoors |
| 20 mil | Heavy-duty | Under-slab barriers, permanent liners, greenhouses | 5-10 years with reinforcement |
6 mil plastic works adequately for indoor projects or short-duration outdoor use, handling moderate temperature swings and light wear. However, it crumbles under the sustained assault of construction sites or long-term outdoor exposure.
10 mil sheeting bridges the gap—thicker than 6 mil by about 67%, offering improved tear resistance. Yet it still falls short when projects involve sharp objects, heavy foot traffic, or multi-year outdoor exposure.
20 mil reinforced plastic enters a different category entirely. The combination of thickness and internal string reinforcement means it won’t shred into ribbons when wind catches an edge—a common failure mode for thinner plastics.
Cost vs. Performance Trade-offs
Thicker plastic contains more polyethylene, driving up material costs proportionally. A 20 mil roll costs significantly more than 6 mil equivalents. However, the durability equation favors thick material for permanent installations. Replacing failed 6 mil barriers twice often exceeds the upfront cost of one 20 mil installation that lasts a decade.
Benefits of Choosing 20 Mil Plastic
Unmatched Puncture Resistance
When vapor barriers encounter broken concrete, protruding rebar, or aggregate with sharp edges, 20 mil thickness simply absorbs the abuse. The material flexes around obstacles rather than tearing—critical for maintaining the continuous barrier that prevents moisture transmission.
Energy Efficiency and Cost Savings
Thick vapor barriers pull double duty as insulation supplements. Buildings with 20 mil crawl space barriers can save up to 20% on heating and cooling costs by preventing air infiltration and moisture that requires extra HVAC work to manage.
Longevity That Justifies Investment
UV-resistant 20 mil reinforced sheeting maintains integrity for 5 to 10 years outdoors. The polyester reinforcement prevents the catastrophic tear propagation that destroys thinner films—when reinforced plastic punctures, the hole stays localized instead of racing across the entire sheet.
Health and Safety Protection
Since approximately 40% of indoor air originates from crawl spaces, a robust 20 mil barrier blocks allergens, animal waste, mold spores, and radon gas from infiltrating living areas. This thickness provides peace of mind that thinner materials simply cannot match.
Installation Considerations
Handling and Deployment
20 mil reinforced sheeting arrives as a heavyweight product—literally. Larger installations require multiple people to unroll and position the material. The stiffness that provides durability also makes it less conformable than 6 mil alternatives, requiring patience when wrapping complex shapes.
Sealing and Joining
Seams remain the weak point in any vapor barrier system. For 20 mil installations, use compatible tape specifically rated for thick plastic—standard construction tape may not adhere properly to the texture created by string reinforcement. Overlap seams by at least 6 inches and seal completely to maintain the continuous barrier.
When Thinner Options Suffice
Not every project justifies 20 mil thickness. Temporary indoor applications, short-term outdoor covers lasting weeks rather than years, or budget-constrained projects with minimal puncture risk can use 4-6 mil sheeting effectively. Reserve the heavy-duty material for scenarios where failure carries significant consequences or replacement proves impractical.
Key Takeaways
- 20 mil plastic measures 0.02 inches (0.508 mm) thick—roughly equivalent to 20 sheets of paper stacked together, making it the heavyweight option for demanding applications
- Reinforced versions contain polyester string mesh that prevents tear propagation, allowing the material to maintain integrity even when punctured
- Durability spans 5-10 years outdoors with UV protection, compared to single-season lifespans for construction-grade alternatives
- Primary uses include under-slab vapor barriers, greenhouse covers, aquaponic liners, and landfill containment where puncture resistance and longevity justify the higher cost
- Energy savings reach up to 20% when used as crawl space vapor barriers, doubling as insulation while blocking moisture and radon gas
Frequently Asked Questions (FAQ)
How thick is 20 mil plastic in simple terms?
20 mil plastic measures exactly 0.02 inches or 0.508 millimeters thick. To visualize this, imagine stacking 20 sheets of standard paper together—that approximates the thickness you’re working with. It’s about two-thirds the thickness of a standard credit card, which measures 30 mil.
What is the difference between 10 mil and 20 mil plastic sheeting?
20 mil is exactly twice as thick as 10 mil—doubling the polyethylene content and substantially increasing puncture resistance, tear strength, and lifespan. While 10 mil works for moderate construction applications, 20 mil handles extreme conditions like under-slab installation where sharp rocks and heavy equipment traffic would destroy thinner materials. The cost doubles, but durability can extend from 1-2 years to 5-10 years for reinforced versions.
Can 20 mil plastic be used as a greenhouse cover?
Absolutely—20 mil string-reinforced plastic makes excellent greenhouse covering when it includes UV stabilizers. The thickness and reinforcement withstand wind, snow loads, and accidental impacts that would shred 6 mil alternatives. UV-rated 20 mil sheeting lasts 5-10 years in full sun exposure, making it cost-effective for permanent greenhouse structures despite the higher upfront investment.
Why is 20 mil plastic recommended for vapor barriers?
20 mil vapor barriers provide superior puncture resistance and extremely low permeability essential for preventing moisture transmission through concrete slabs and foundation walls. The thickness survives rough construction conditions—workers walking on it, dropped tools, sharp aggregate—without compromising the continuous barrier. It also effectively blocks radon gas infiltration, which thinner films cannot reliably stop.
How long does 20 mil plastic sheeting last outdoors?
UV-resistant, string-reinforced 20 mil plastic typically lasts 5 to 10 years outdoors, depending on sun exposure intensity and weather conditions. Standard construction-grade 20 mil without UV protection degrades within 1-2 years. The polyester reinforcement prevents complete failure even as UV rays gradually weaken the polyethylene—instead of disintegrating into shreds, reinforced plastic develops small cracks while maintaining overall integrity.
Is 20 mil plastic sheeting worth the extra cost?
20 mil justifies its premium price for permanent installations and applications where failure carries significant consequences. For temporary projects lasting weeks or indoor use with minimal puncture risk, 6 mil saves money without sacrificing performance. The decision hinges on durability requirements—replacing failed barriers twice often costs more than installing 20 mil once and forgetting about it for a decade.
What does “reinforced” mean in 20 mil plastic sheeting?
Reinforced sheeting contains internal layers of polyester string cord arranged in a cross-hatch pattern throughout the plastic. This engineering transforms behavior during puncture—instead of tearing completely across the sheet when impaled, the string mesh stops tear propagation, containing damage to the immediate puncture area. Think of it as rebar in concrete—the reinforcement doesn’t prevent all damage, but it prevents catastrophic failure.
Quick Navigation