| http://www.w3.org/ns/prov#value | - a) the foam of at least one water-soluble polymer having a weight per liter of from 10 to 1,000 g/l is prepared, and the foam is spread in a sheet-like fashion at a layer thickness of from 1 ??m to 100,000 ??m, preferably from 10 ??m to 10,000 ??m, and particularly preferred, from 200 ??m to 5,000 ??m,
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