Vermiculite Horticultural Grade - CLASS B

Vermiculite is an excellent soilless planting medium. It is non-toxic sterile moist resistant and has a nearly neutral pH. What's more, the material is very lightweight and able to hold water very well, which is quite contrasting to perlite. Yet, it does not keep aeration as well as perlite.
This growing media also has a reasonably great cation-exchange capacity, which helps keep the nutrients for later use.

There are different vermiculite types, so bear that in mind and choose the correct material for the hydroponic purpose.

And because of its ability to retain much water (approximately 200%-300% of its weight), there's a risk of suffocating your plants. So it is usually used to mix with other mediums. The most familiar one would be perlite as the two media complement each other quite well - perlite drains so fast whereas vermiculite holds moisture.
They are often conjuncted in a 50/50 formula, which keeps the mix from being washed away in ebb and flow systems.

Can be used in the drip system, aeroponic system. 

Benefits:

Water and nutrient retention
Downsides:

Poor drainage capacity
Danger of suffocating plants