Chromatin is the generic term for DNA (not "fiber") wound around proteins called histones. From the description you've given, it sounds like you're talking about euchromatin.

There are generally two types of chromatin: euchromatinand heterochromatin. Under the microscope, heterochromatin tends to stay at the periphery of the nucleus, while euchromatin tends to stay central in the nucleus. Also microscopically, euchromatin is a bit lighter (ie, it doesn't stain as heavily) than heterochromatin, reflecting the fact that euchromatin is less dense than heterochromatin. The decreased density has to do with euchromatin being loosely wound around histones, whereas heterochromatin is wound rather tightly. Heterochromatin also has a number of other chromatin-modifying proteins around that prevent it from coming undone easily.

The functional difference between the two types of chromatin has to do with how effectively DNA transcription (the process by which DNA is transcribed to RNA) can occur. The dense heterochromatin is so tightly wound and so tightly packed with associated proteins that the DNA transcription machinery can't get access to the DNA contained within the heterochromatin. Only the loosely wound euchromatin will permit the machinery to gain access to its DNA. Therefore, generally euchromatin contains DNA that is being actively transcribed, while heterochromatin is transcriptionally silent.

THE ANSWER IS CHROMATIN!!