Abstract: Structure of semifinished product (10) for floating products comprising a plurality of layers (1a-Id) of flexible material having density less than water, for example foam polyethylene, mutually constrained to each other. In particular, the layers (1a-Id) are arranged according to an overlapped configuration and then constrained at fastening points, for example, seams (6) made by a stitching head (50) equipped with one or more needles (55) acting along a direction (60) substantially orthogonal to the layers (1a-Id). Each seam point (6) is, in particular, insulated, i.e. is made in order to result distanced from the other seams (6). This is to avoid the production of weakening lines, or zones, in the semifinished product (10) and to obtain, then a highly flexible product and at the same time having a high mechanical resistance. The seams (6) can be made in a random way or following a predetermined scheme to provide a homogeneous distribution on all the surface of the layers (1a-Id).