If you have read the phrase "4-way stretch" anywhere, you might find the meaning easy enough to guess, but there's definitely more to it.
There are actually one-way, two-way and four-way stretch fabrics.
To understand the differences, you would need to know that the deciding factors are a fabric's 1) stretchability and 2) recovery.
One-way stretch means a fabric will stretch side to side but will not recover. Interlock knits and jersey without Lycra are good examples.
Two-way stretch means a fabric stretches side to side but recovers. Hence the "two" part - stretch and recover. Jersey knits with Lycra are an example.
Four-way (or 4-way) stretch means a fabric stretches and recovers both width and lengthwise. Fabrics using or that are nylon/Lycra are an example of four-way stretch fabric.
Fabric that are 4-way stretch provides freedom of movement to its wearer.
People who are wearing 4-way stretch fabrics are capable of small active movements such as jumping, running, and biking.
Fully stretchable qualities make clothing very wearable and comfortable.
My colleagues wear our Motile Pants literally everyday. They even tested them out at the rock climbing wall, on their bikes, or when they go out for a jog. The results? Wonderfully surprising, as the 4-way stretch allows them to move freely in almost every activity they try. Traveling on long flights also isn’t a nuisance anymore since the pants are incredibly stretchy and provides supreme comfort, not to mention has amazing water repellent qualities.