The invention provides a dust-proofing material which has excellent dust-proofing properties and can follow even clearances of as minute as 0.10 to 0.20mm by virtue its excellent flexibility. The invention relates to a dust-proofing material constituted of a foam having a thickness of 0.1 to 1.0mm, characterized in that the foam has micro-cellular structure having a mean cell diameter of 10 to 65[mu]m and exhibits such characteristics as to give a repulsive load of 0.010 to 0.100MPa when compressed to a thickness of 0.1mm and an apparent density of 0.01 to 0.050g/cm3. It is preferable that the foam have either closed cell structure or semi-open and semi-closed cell structure. The foam may be provided with a pressure-sensitive adhesive layer on either or both of the sides. It is preferable that the pressure-sensitive adhesive layer be formed on the foam through a film layer.