A non-curling laminar body, esp. a see-through casing, consists of 2 superimposed polymer films, connected together by =1 welded seam. The polymer film consists of an unstretched, tempered polymer contg. polypropylene, and the temp. at which the seam is welded is such that the seam has a morphological structure about the same as that of the tempered polypropylene-contg. polymer. The tendency for the film to become corrugated or to slip on the line of the seam is reduced. Other properties, e.g. tear strength and dimensional stability at increased temp., are improved.
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