When custom framing, mostly it is necessary to create some separation from the art and the frame for the perfect effect. Matboard is used to add this separation. It is made of thick cardboard and its color supplements or highlights the picture. Because matboard is paperbased and usually used for framing works on paper (print, copper engraving, photo, aquarelle etc.), glass is added to protect the finished work from external influences.
There is a solution for arts which matboard and glass are never used for, for example oil painting or relief. In this case, liner is used between art and frame. The liners are narrower than the frame and are made by painting a wood frame or wrapping it in fabric. Linen liners have been used for centuries for oil paintings.