The invention is a decorating medium, system and method for producing relief art on substrate surfaces. The decorating medium is an acrylic emulsion based medium containing an expandable polymer which expands the medium upon heating. The acrylic emulsion is produced with a mixture of an acrylic binder and an acrylic thickener or a cellulosic thickener combined in the appropriate range to obtain a medium rheology suitable for controlled application of the medium to the substrate surfaces. The decorating medium is applied to a substrate surface in a desired pattern either directly from a storage bottle or tube equipped with a nozzle or with an applicator such as a brush, a sponge, a knife or spatula. The desired pattern is achieved by free hand or by using a stencil or mask. After the decorating medium is applied to the surface of the substrate in the desired pattern, the medium is cured and heated. The heat causes the medium to expand and creates the relief art on the surface of the substrate. The relief art is flexible after curing and may be painted or decorated according the needs and taste of the artist. In an alternative embodiment of the invention, the decorating medium is mixed with decorating additives of choice such as pigments, colorants or glitters, prior to curing and heating the medium. The medium, the system and the method of the current invention are particularly useful for creating relief art on cloth or fabric substrates, but are also suitable for creating relief art on other substrate surfaces including metal, plastic, paper, cardboard and glass surfaces.