Skins available to a control are contained in one or more skin files in a theme directory. The Control.SkinID property specifies which of these skins to apply to the control. A skin is specific to a particular control; you cannot share skin settings between controls of different types.

If you do not set the Control.SkinID property, a control uses the default skin if one is defined. For example, if a skin without an ID is defined for an System.Web.UI.WebControls.Image control, then that skin applies to all System.Web.UI.WebControls.Image controls that do not explicitly reference a skin by ID and that are not set to disable themes. If a skin with an ID is defined for an System.Web.UI.WebControls.Image control, then that skin applies only to System.Web.UI.WebControls.Image controls whose Control.SkinID property is set to that ID.

If the skin files in a theme directory do not contain a skin with the specified Control.SkinID property, an ArgumentException exception is thrown at run time.