The Grid technology is a woven configuration of Hytrel filaments which provide superior cushioning and stability by centring the heel when impacting the floor.
Saucony uses the GRID system because unlike other cushioning systems seen in technical running shoes, it offers stable cushioning. If you notice that when running the first part of the foot hitting the ground is the heel, so this is vital to the health of a runner due to the fact that when the heel touches the ground a force of up to three times body weight (3G) is generated. This force acts not only in the heel but also it is transmitted up the lower leg and into the back, affecting the ankle, knee and hip joints.
The GRID cassette fits into the rearfoot section of the midsole (as shown on picture below), as the impact occurs, the interwoven Hytrel strands bend to the shape of the heel, while the midsole compresses, thus providing cushioning.
Which let this technology be one of the best for running is that the actual user is more in control of the cushioning movement. GRID Technology = Controlled Cushioning