This is the HO Scale Sidewalk 300 Scale Feet by Bar Mills.
HO and N Sidewalks Made Easy
Bar Mills has solved a modeling dilemma for N Scale modelers: adding realistic sidewalks to street scenes. Sidewalks from Bar Mills are made from a specially imported paper material that has the proper texture and thickness. The sidewalks come precolored in a dirty concrete color, are laser-cut to size and include laser-etched crack and curb lines. The material is flexible, so applying them to your layout surface is easy even if there are grades or surface irregularities along the pavement's edge.