Interstellar gas and dust

What is the interstellar medium? What is the composition of interstellar gas? Of interstellar dust? The outer space is not a vacuum. The space between stars is filled. The martials which fills the space between the stars is called Interstellar medium. This martial is composed of approximately 99 percentage of gas (90% of it is molecular or atomic hydrogen, 9% is helium) and 1 percentage of dust. The composition of interstellar dust is not very well known to scientists although they say they have infrared evidence for silicates, graphite and iron in it.