Frost cloth, also known as a row cover or floating row cover, is a lightweight textile engineered to shield plants from cold temperatures and frost damage. This specialized fabric creates a warmer microclimate around vegetation by retaining the earth’s heat that radiates upward at night. Understanding its composition is necessary for selecting the appropriate cover to extend a growing season or protect vulnerable plants from an unexpected freeze.
Primary Material Composition
Most commercial frost cloth is manufactured using synthetic polymers, which are essentially plastic fibers. The dominant material is polypropylene, a thermoplastic polymer chosen for its light weight and low production cost. Polypropylene is durable and resists moisture, making it ideal for outdoor agricultural applications.
While polypropylene is the standard, some covers may incorporate less common synthetic fibers like polyester. These materials are extruded from melted polymer granules to form fine, continuous filaments, ensuring the raw material has the necessary strength and flexibility before assembly.
Manufacturing Structure and Permeability
Frost cloth is typically a non-woven fabric, meaning it is not created by weaving yarns together. It is generally produced using spun-bonding, where continuous filaments are laid down randomly to form a loose web. Heat and pressure bond these fibers together, resulting in a cohesive, porous sheet.
This non-woven structure allows air and water to pass through freely. The porous nature permits rain and irrigation water to reach the soil and allows for proper ventilation, which prevents excessive humidity and fungal growth beneath the cover. The sheet also allows sufficient light transmission for photosynthesis, unlike opaque materials such as blankets or plastic tarps.
Weight Classifications and Thermal Rating
The effectiveness of frost cloth is tied to its density, measured in ounces per square yard (oz/yd²) or grams per square meter (gsm). Density determines the material’s insulating capacity and light transmission.
Light Weight (0.45 to 0.60 oz/yd²)
These are considered summer or season extension covers, offering minimal frost protection but maximum light transmission (around 85-90%). They are often used for insect exclusion or providing a few degrees of thermal benefit.
Medium Weight (0.9 to 1.5 oz/yd²)
These fabrics are suitable for season extension and moderate cold protection. A 0.9 oz/yd² cover might provide 4 to 6 degrees Fahrenheit of frost protection, while transmitting about 70% of available light.
Heavy Weight (1.5 oz/yd² to 2.5 oz/yd²)
These covers are designed for serious freeze protection. They can protect plants down to temperatures as low as 24°F, offering 8 to 10 degrees or more of temperature increase. This increased insulation comes at the expense of light transmission, which can drop to 50% or less.
Material Additives and Lifespan
Because frost cloth is primarily made from polypropylene, a material sensitive to solar damage, manufacturers incorporate specific additives to ensure durability. The primary component added is an Ultraviolet (UV) stabilizer, mixed into the polymer granules before spun-bonding.
Without these stabilizers, polypropylene fibers degrade rapidly when exposed to direct sunlight, losing up to 70% of their tensile strength within a year. Stabilizers, such as hindered amine light stabilizers (HALS) or zinc oxide, work by absorbing or blocking the UV radiation that breaks down the polymer chains. This prevents the material from becoming brittle, weak, and tearing apart after one season. UV-stabilized frost cloth can last for multiple growing seasons, increasing the product’s longevity.