Fibrous sheets are coated or impregnated with a biodegradable composition to render the sheets more resistant to penetration by liquids. Biodegradable polymer blends suitable for use in coating or impregnating a fibrous sheet can be manufactured from at least one type of polyhydroxybutyrate, optionally in combination with at least one additional biodegradable polymer (e.g., a "hard" biodegradable polymer having a glass transition temperature of at least about 10.degree. C. and/or a "soft" biodegradable polymer having a glass transition temperature less than about 0.degree. C. Sufficient inorganic filler may be included so as to render the treated sheet microwaveable. The biodegradable polymer compositions are especially well-suited for coating or impregnating paper sheets, e.g., 12-15 lb/3000 ft.sup.2 tissue paper to yield food wraps. Food wraps will typically be manufactured to have good "dead-fold" properties so as to remain in a wrapped position and not spring back to an "unwrapped" form.