When the control is resized, it updates the layout grid so it always fills the control's client area. Normally, this is done by scaling every band and keeping their proportion constant.

In some cases, however, you may want to keep the size of a band constant, and let the other bands shrink or expand to accommodate the new control dimensions. For example, you may have a row that contains constant-size headings, and should not be resized with the control. In these cases, set the IsFixedSize property to true and the band will not be resized when the control dimensions change.

The IsFixedSize property prevents the control from resizing the band when the control is resized. It does not prevent the user from resizing the band with the mouse if the IBand.IsSplitter property is set to true.

Reference

Band Class
Band Members