Right Mil Thickness For Your Crawlspace Vapor Barrier

Right Mil Thickness For Your Crawlspace Vapor Barrier

Vapor barrier thicknesses range from 6 mil to 20 mil, with 6 mil being the bare minimum and 20 mil being the most heavy duty and puncture-resistant.

Read on for more information on what vapor barrier thickness is right for your project.

Why a Crawlspace Vapor Barrier?

Sealing an open crawlspace with a vapor barrier can prevent moisture accumulation in your floors and living space, saving your home from wood rot and mold. Crawlspace encapsulation can also lead to significant energy savings.

Read more: Does Your Crawlspace Need a Vapor Barrier?

Crawlspace Vapor Barrier Material

Reinforced polyethylene plastic sheeting (poly) of at least 6 mil thickness is the material most commonly used as a vapor barrier. This liner offers a balance of value and durability, but is the bare minimum in thickness for a vapor barrier. Reinforced poly comes in a variety of thicknesses and strengths.

Poly stocked at the local hardware store is often thinner, non-reinforced, and could be made out of recycled or “regrind” poly. Regrind poly may contain impurities such as dirt or moisture. While thinner plastic or regrind may be OK for short-term use, only reinforced virgin poly should be used for long-term applications like crawlspace vapor barriers. Properly installed virgin reinforced poly should last 20 years or more in a crawlspace.

Read more: Virgin vs. Regrind in Poly – What is the Difference and Why is it Important?

Crawlspace Vapor Barrier Thickness

There are two measurements you should be familiar with when choosing your poly. Mils is the measurement of the poly’s thickness, and perms represents permeability to moisture.


Polyethylene sheeting is measured in “mils.” 1 mil is equal to 0.001 inch of thickness. Our standard recommendation for most residential applications is a 6 mil (0.006-inch thick) reinforced poly vapor barrier. Americover offers thicknesses all the way up to 20 mil.


The perm rating represents how readily water vapor will pass through a material. The lower the perm rating, the less permeable a material is. To classify as a vapor barrier, a material must have perm rating of 0.1 or below. Poly sheeting that is 6 mils (0.06 perms) and thicker meets this definition.

Choosing your Crawlspace Vapor Barrier

The thickness of poly you choose will mainly depend on two factors:

  • Utilization of the crawlspace (storage, maintenance, etc.)
  • Soil or material on the floor of the crawlspace

If the crawlspace is going to be entered regularly for maintenance, or if items are going to be stored in the crawlspace, it is a good idea to get a thicker poly, such as 12 mil. The bare minimum 6 mil is also inadequate if the floor of the crawlspace has rocks, roots, or concrete chunks. Remember that one tear or puncture in your vapor barrier will allow moisture to pass through and render the barrier less effective.

To save cost without sacrificing durability, you can use a thinner poly, such as a 6 mil or 8 mil, on the walls of the crawlspace, while using a thicker poly on the floor.

List of Americover Crawlspace Liners

All of Americover’s vapor barriers are string-reinforced 100% virgin poly.

6 mil String-reinforced Crawlspace Liner

String-reinforced 6 mil is an economical choice when the overriding concern is cost. However, 6 mil is not recommended for areas where there will be activity or there are rough surfaces.

8 mil String-reinforced Crawlspace Liner

String-reinforced 8 mil works well over soils made of dirt, mud, clay, or sand. Our 8 mil is frequently used on the walls in conjunction with a heavier material on the floors.

10 mil String-reinforced Crawlspace Liner

String-reinforced 10 mil is an economical choice that performs much better on the walls of a foundation and can be used on the ground when there will be no activity taking place in the crawl space.

12 mil String-reinforced Crawlspace Liner

Because of its puncture resistance, string-reinforced 12 mil is great for soils that are rough or contain small rocks or tree roots, or for crawlspaces where there will be light or moderate activity. This film is an excellent choice when you need to strike a balance of economy and quality.

Antimicrobial 12 mil String-reinforced Crawlspace Liner

Although all polyethylene is inherently antimicrobial, this crawlspace liner is specially treated to prevent the growth of harmful bacteria, fungi, mold, and algae. Tuff-Scrim TS12-AM’s antimicrobial additive is blended into the poly to make it non-migratory, wash-resistant, non-toxic, and environmentally safe. Tests have proven that fungi will not grow on, near, or around TS12-AM.

20 mil String-reinforced Crawlspace Liner

String-reinforced 20 mil is one of the thickest and toughest films on the market. It is great for commercial applications where an extra heavy-duty product is required. Its puncture resistance makes it great for use over soils that are hard or contain large rocks or broken concrete. Our 20 mil is the best product to use where there will be heavy activity.

More Information

Read more about how to choose, measure, and install a crawlspace liner.

If you are still unsure which size is best for your application, please call to speak with a representative today at 760-747-6095, or email us at sales@americover.com.