The thickness of a crawl space vapor barrier typically ranges from 6-mil to 20-mil, with the ideal thickness depending on your specific needs for durability and moisture protection:

• 6-Mil Polyethylene: This is the most economical and widely available option. While it meets basic building codes, it offers minimal protection and is prone to tearing.
• 12-Mil Polyethylene: This is the recommended baseline for most residential applications. It provides dependable puncture resistance and better withstands the seasonal expansion and contraction of the crawl space.
• 20-Mil Reinforced: This heavy-duty option is used for professional encapsulation. It is highly durable, offers excellent vapor resistance, and is ideal for high-moisture areas or spaces used for light storage due to its superior resistance to foot traffic and mechanical damage.

Thicker, reinforced barriers generally offer the greatest longevity (often 20+ years) and the best protection against moisture-related issues like mold and structural rot.