A method of producing polyurethane foam filter material containing an activated carbon adsorbent which comprises reacting a polyurethane foam-forming composition comprising isocyanates and polyesters or polyethers in the presence of particles of an activated carbon adsorbent, a small amount of water and a catalyst, characterized in that the particles of the activated carbon adsorbent are pre-coated on their surfaces with a film-forming polymeric material which does not substantially react with the polyurethane foam-producing components, does not dissolve the polyurethane foam and can be removed, after formation of the polyurethane foam, by application of solvent. The filter material obtained finds a wide range of utility such as for water cleansing, ion-exchanging, deodorizing or drying purposes.

Microporous sheet structures are provided and a method for their production which comprises reacting an organic polyisocyanate with an organic compound containing at least two hydroxyl or amino hydrogen atoms reactive with NCO groups as starting materials to produce a polyaddition product which in the homogeneous state exhibits a shore A hardness greater than 40 and a softening range above 100.degree.C. The said reaction is effected in an organic liquid which dissolves the starting materials, does not dissolve the polyaddition product, boils below 250.degree.C and contains 1 to 300 percent by weight, based on the polyaddition product to be formed, of a polar solvent which is inert to the starting materials. Said polar solvent has a greater evaporation number than the components of the aforesaid organic liquid (in the following called nonsolvent), the nonsolvent being such that while the polyaddition product forms, it gradually becomes increasingly insoluble in the mixture of polar solvent and nonsolvent. This mixture has no significant swelling effect upon the polyaddition product.

Addition of small amounts of acidic silica to improve hydrolytic stability of polyurethanes.

Inorganic-organic compositions obtained from a mixture of components comprising: (a) from 5 - 98% by weight of an organic polyisocyanate (b) from 2 - 95% by weight of an aqueous silica sol containing about 20 - 60% by weight of said silica and, (c) from 0 - 93% by weight of a water-binding component Based on the total weight of (a), (b) and (c). The products of the invention may be used in many forms including both porous and non-porous products as surface coatings having good adhesion and resistance to abrasion, as a mortar, and as a foam concrete for making molded products particularly in construction engineering and civil engineering as for building walls, igloos, road building and the like.

A package comprising a dessicant material consisting essentially of 1 a dessicant and 2 tough, film-forming, resin having a high moisture vapor transmission rate. A prepolymerized polyurethane is particularly useful. The material is of particular value as a package insert - e.g. with film or cameras or as a coating material which can be utilized on equipment to be protected or, most advantageously, on the interior walls of packaging boxes and the like.