foam plastics sheet material , such as a wallcovering , has a pronounced decorative relief finish and comprises a substrate web with a foam coating some at least of which is blistered . the blistering is achieved by having two foamable coatings on the web , the lower of which is sacrificed to produce the blistering in the upper . in one method the lower coating is foamed , the upper coating is then applied in its pre - foamed state , and then heated so that the lower coating is sacrificed and the upper coating is foamed and blistered . in another method both coatings are applied in their unfoamed state with the lower coating having a lower foaming temperature than that of the upper coating . both coatings are then heated together . the lower coating foams and is then sacrificed . the upper coating foams and blisters .