Abstract: A mold tool having at least two parts, a first part and a second part. The first part and the second part are releasably coupled to configure an outer mold structure and an inner mold structure. The outer mold structure and inner mold structure is high strength alloy for example high strength steel. A low melt alloy is disposed within the inner mold structure as an inner material such that low melt alloy provides an evacuable interior space. The evacuable interior space surrounds and accommodates an insulated winding bar. The dimension of the insulated winding bar determines the shape and dimension of the low melt alloy in the inner mold structure.

Abstract: A folding swim fin which comprises a base, arms, an elastic membrane tensioned between the arms and elements for attaching the fin to the swimmer's feet. Two opposite edges (1 and 2) of the flexible membrane (3) are attached each to one elastic strip (5). The flexible membrane (3) is made of plastic material, preferably reinforced with fibres. A preferred variant of the invention is a membrane woven with durable fibres. The strip (5) is attached to a rigid beam (6) of the base, belonging to a pair of beams connected to each other by a hinge (7) placed at a distance of 0 to ? of the beam (6) length from the beam end opposite to the place of the strip (5) attachment.