Fibrous astrocytes are found primarily in white matter, have a smoother cell body contour than do protoplasmic astrocytes as seen with glial-specific stains, and have processes that tend to emerge from the cell body radially. These processes are narrower and branch to form end feet on blood vessels, ependyma, and pia. Consequently, the processes of fibrous astrocytes do not form sheets and do not tend to conform to the shape of the surrounding neurons or vascular elements. The major distinguishing feature of fibrous astrocytes, as the name suggests, is an abundance of glial fibrils arranged in parallel arrays in the cytoplasm and extending into the processes.
In Nissl stains, the fibrous astrocytes have a nucleus essentially the same as that of the protoplasmic type with a flecked appearance. Intercellular adherences have also been observed between fibrous astrocytes.