RadFilter uses skins to control its overall look-and-feel. A skin is a set of images and a CSS stylesheet that can be applied to the control elements (items, images, etc.) and defines their look and feel. By default all controls in Telerik controls for ASP.NET AJAX suite have a polished look and feel which is consistent across the whole product line.
These are the skins provided by Telerik. They are embedded in the Telerik.Web.UI.dll assembly as web resources. To use a built-in skin the user only needs to set the Skin property of the control. Built-in skins are also provided in "C:\Program Files\Progress\UI for ASP.NET AJAX RX YYYY\Skins".
Below is a set of the Telerik RadFilter skins:
The Material skin is available for the Lightweight RenderMode only. If you experience visual issues with it, make sure your controls are not using the default Classic mode.
The Hay , Forest , Sitefinity and Transparent skins are obsolete and have been removed from the Telerik.Web.UI.Skins.dll assembly as of Q1 2014 . You can find more information on the matter inthis blog post.
These are skins created by the developer. They are not embedded so the control cannot register them automatically. If you use a custom skin you need to set the Skin property, and the EnableEmbeddedSkins property of the control to false. If you do not do so, an exception will be thrown saying that there is no embedded skin matching the Skin property
Please examine the Creating a custom skin help topic for additional information.