The patented envelope system consists of a layer of specially selected sand or stone wrapped in a strong but highly porous membrane. This prevents erosion but allows moisture to pass through at a very high rate.
A high drainage rate has two major benefits. First, standing water is not a problem provided the surfacing material is porous to allow water into the base. Second, as little water remains within the base, the effects of frost heave are minimized.
The material in the envelope is selected so that particle size, shape, and distribution do not allow over compaction or settling out. As a result, the playing characteristics and drainage capabilities are maintained over a long period. Since 1981, experience in the United Kingdom has shown that the system matures the longer it has been down.
The special geotextile “Nottsfilm” that encases the sand or stone, has been especially developed to allow for high porosity and enable particulate material to be retained. It is a resin-bonded, needle-punched, polyester fabric only 1 to 2 mm thick yet its load-bearing capabilities are so good that only one layer is normally required. The pore spaces in the material are evenly distributed, thus, giving consistent drainage throughout the material.
By using natural paniculate materials as the base, construction is similar to a natural turf pitch with a synthetic turf surface. This combination results in playing characteristics close to those of natural turf being achieved on an installation with the usage capabilities of synthetic turf. Tests carried out in United Kingdom meet the requirements of the Winterbottom report for soccer pitches.
Injuries associated with synthetic turf areas consist primarily of either stress-related injuries to the limbs or friction burns. On conventionally constructed engineered bases, it is very difficult to eliminate these factors, as solid base construction contributes to both injuries. The envelope system is better on both counts. First, the natural impact absorption properties mean that the stresses caused by interactions with the surface are similar to those exhibited by natural turf pitches. Second, the possibility and degree of friction burns are reduced because much of the energy is dissipated into the air spaces between the materials in the base leaving less energy available to be turned into heat.