A method for forming a sealed cell structure is disclosed. The sealed cell structure comprises first (10) and second (12) substrates that are spaced apart by a plurality of partition walls (14). The partition walls define a plurality of cells (18, 19) between the first and second substrates. At least one of the substrates and the partition walls have a layer (16, 22, 30) of photo-embossing material on them. A latent image is written (112) onto the photo-embossing material, and then the image is developed, thereby causing expansion of the photo-embossing material in the areas (114) according to the pattern of the latent image. The expansion of the photo-embossing material causes the cells to be sealed apart from one another.