Tarp types Tarps come in many different materials, sizes, and thickness. Photo: Ryan Maher. Tarps come in different materials, sizes, and thicknesses and vary in permeability, cost, and longevity (Table 1). For occultation, polyethylene silage tarps—made for excluding light and water from silage bunkers—or “ag plastic” are most commonly used because they are cost-effective, durable,