a container made of a synthetic material , e . g ., a bottle , comprising a closed bottom wall and an opening in the upper portion opposite the bottom wall . the container is produced according to a blow moulding , stretch blow moulding or thermoforming method , and its wall comprises at least one fold line consisting of a narrow linear area of said wall , in which the synthetic material has a different physical structure , whereby it is less plastically deformable but has at least as much tensile strength as the rest of the wall . this structural modification is obtained by mechanical or thermal processing or by exposure of the area in question to suitable particle radiation . the resulting bottle is readily foldable with a view to disposal after use .