String Trimmer Line Shaping
The shape of the line also affects the cutting efficiency. String trimmer line comes in a variety of shapes: round, twisted, square, star shaped, and serrated. Rounded line is the most common type available, but it because it lacks a cutting edge, it rips the grass rather than cutting it. Twisted line is a bit better, as the shape has a little more of a cutting edge to it.
Some line comes in a square or star shape. The edges of these string trimmer lines are sharper than rounded trimmer line, and cut through the grass rather than tear at it. Serrated line is also an option when it comes to sharper trimmer line. It has teeth, similar to a kitchen knife, and saws through heavier grass and weeds with relative ease.
String Trimmer Line Material
Nylon line is the most common line available, but it tends to wear out and break quickly on anything but lighter duty jobs. Manufacturers have come out with a variety of alternatives for heavier duty jobs, however. Some examples include reinforced composite nylon, internally reinforced nylon, and aluminum additives for added strength.
Although not line in the technical sense, some of the beefier string trimmers can work with nylon, or even metal, blades. All of these options improve the durability of the light gauge nylon string, but if the vast majority of your trimming work centers on light grass clipping, you can probably get by with cheap, simple nylon line.