Synthetic Turf | Understanding The Basics
by Erik Spring, PLA
Synthetic turf fields are everywhere from the NFL to little league soccer fields. I’ve designed many synthetic turf athletic fields for parks and school districts (see some projects here). After working with maintenance staff, turf manufacturers, athletic directors, students and recreational athletes, I have a good idea of the pros and cons of the most common synthetic turf options.
Lace up your cleats and I'll help you understand the basics of synthetic turf and which turf will work best for your field. To keep this simple I'll keep this focused on athletic turf. Other types of turf include playground surfacing, residential applications, pedestrian spaces (plazas), etc.
If you need more detailed information, I've included some resource links at the end, or leave a comment and I'll get in touch.
Most synthetic turf is made of one of the following three fiber types:
Single blades of fiber that stand up straight, sometimes with a thickened spine or edges to help them stand on end. Monofilament turf is the best looking turf because the blades stay upright longer. It can be great for baseball because the upright fibers lend themselves to a slower ball roll, but the nature of individual fibers means there tends to be more infill splash, so it may not be ideal for soccer.
The Verdict: Ideal for baseball, football or lacrosse.
2. Slit Film
Extruded tape-like flat strands that are sliced (slit) forming a honeycomb-like fiber. Once the turf system is installed, the tops of the strands break apart (or ‘filibrate’) creating a more natural looking surface. Slit film turf holds up to high use activity better than monofilament. It tends to provide a faster ball roll and less infill splash.
The Verdict: Ideal for soccer and multi-use fields.
The best of both worlds: hybrid systems include a combination of monofilament and slit film turf fibers.
The Verdict: Great for soccer and multi-use athletic fields.
Infill material fills the gaps between the fibers
If you took a sheet of synthetic turf off the manufacturing line and laid it on the ground, the fibers would fall over and lay flat. Enter the infill.
Infill fills the voids between the turf fibers or tufts (groups) of fibers. After infilling only about 1/2” of turf fiber is left exposed. Infill also weighs down the turf, and provides impact attenuation (softening falls) reducing injuries. The material used for infill varies but is most commonly a mixture of silica sand and SBR rubber (usually made from recycled car tires), however synthetic turf technology evolves quickly; this could change at any time.. The ratio of sand to rubber can vary depending on the desired firmness of the field. More sand yields a firmer, faster field while more rubber gives a softer feel but will tire out your legs quicker.
There are synthetic turf products that don’t require infill material to be added but these systems are not common in athletic field applications. Non-infilled turf uses a thatch zone of thin fibers serving as the soft base layer.
The use of SBR rubber has provoked questions about its application in the past so other types of infill materials have been developed. Alternative infills include coated sand, EPDM, organic materials (cork, coconut, walnut shells), and TPE. The alternative infills offer various benefits and also impact the price of the turf system.
Holding the turf fibers in place
Fibers are punched (or ‘tufted’) through a sheet of fabric holding them together on the sheet. Urethane is then applied on the underside to help hold the fibers in place. The finished product is made in rolls typically 15 feet wide, just like carpet. During installation the rolls are joined by sewing or gluing the seams together to create a continuous field surface.
One exception is woven turf. With woven products, the fibers are woven into the backing rather than tufted. The fibers are fully integrated into the backing on a loom creating an incredible strong product when pulling on the fibers (called ‘tuft bind’). Testing shows woven products are far stronger than tufted products and tend to stand up better on their own (before infill is added). At the time of this writing woven turf is a new technology and I suspect it will quickly become the norm.
We recently included woven turf at the West Fields at Highland Heritage Regional Park and the feedback is overwhelmingly positive. The fields even see regular use by NFL players looking for a top of the line field to practice on their own.
No More Rain-Outs
Once the roll of turf is constructed it’s perforated by punching holes in the backing to allow for drainage. The perforations provide incredible drainage, in the range of 20 inches of water per hour. To put that into perspective, the average rainfall here on the front range in Colorado is around 15 inches-for the year!
Games can be played on synthetic turf in almost any kind of weather. Below the turf a drainage layer, usually crushed rock, allows for water to drain through the turf backing and into a collection system.
Bottom line: within minutes of even a torrential downpour, play can resume on a synthetic turf field. A natural grass field may take hours or even days to dry out enough for play.
Synthetic turf is easy to maintain. There is no need for watering, mowing, aerating, or fertilizing. Synthetic fields mostly need to be groomed (brushed) regularly. Specialized equipment is sold for keeping synthetic turf looking tip top. Grooming cleans the turf (removing sunflower seed shells, etc), keeps the fibers standing up straight and keeps the infill evenly distributed.
This is part of a four-part series on athletic field design. See Dave Peterson's blog for an amazing look at the science behind athletic field design in a post on GIS field analysis. Check back throughout August to see posts on the changes new soccer standards mean for athletic fields and the ins-and-outs of replacing tennis courts.