Strip material with heat-formed hooked heads

In an elongate strip material which can be severed into lengths to form at least a part of a fastener, said strip material comprising a backing having an exposed major surface;

• and a multiplicity of flexible resilient lengths of longitudinally oriented polymeric monofilament, each length including a central bight portion secured in said backing, two stem portions extending from the opposite ends of said bight portion and projecting generally normal to said exposed major surface and enlarged heads at the ends of said stem portions opposite said backing adapted to engage loops projecting from a surface closely positioned in opposition to the exposed major surface of the backing, the improvement wherein said lengths of monofilament have a cross section defining a plurality of radially projecting lobes, and said heads include hook-like portions spaced from said stem portions and projecting a distance along said stem portions toward said backing formed by heating the ends of said lengths of monofilament so that each of said lobes forms one of said hook-like portions and loops from a surface closely positioned in opposition to the exposed major surface of the backing will engage under the hook-like portions of said heads and must be broken before separation of the loops and heads can occur in a direction normal to said exposed major surface of the backing.