When you say it is like material what does that mean. Is it hairy, slimy or does it have another consistancy? A better description might help us to give you a better idea.
If it is hair algae it will be long and thin like fine, straight hair. This type of algae is not harmful but many people do not desire it. It feeds off high nitrates, that could be harming your tank.
Slimy algae will lead us to think it might be cyanobacteria. This is harmful algae. If that is the case, we can go into more detail. I do not think this is the case though.