Annular unframed pleated air filter

A disposable, annular, unframed, pleated air filter, the air filter being configured to be in a compacted shape and being openable to a generally cylindrical, ready-for-use shape, and the air filter comprising:

• a length of pleated air filter media comprising a longitudinal axis and comprising at least one joint so that the length of pleated air filter media is in a continuous annular shape, the pleated air filter media further comprising a transverse axis and exhibiting a pleat direction that is at least generally aligned with the transverse axis, and the pleated air filter media comprising an inward side with inward pleat tips and inward pleat valleys and an outward side with outward pleat tips and outward pleat valleys;
• and,
• at least one adhesive strand that is on the inward side of the length of pleated air filter media and is disposed on the inward pleat tips and penetrates at least partially into at least some of the inward pleat valleys;
• wherein the length of pleated air filter media comprises a first preferred-bending zone and a second preferred-bending zone that is located diametrically opposite the first preferred-bending zone along the longitudinal axis of the pleated air filter media,
• wherein the at least one adhesive strand comprises a first interruption at the first preferred-bending zone and comprises a second interruption at the second preferred-bending zone,
• wherein at least one of the first and second preferred-bending zones is a jointed, non-integral preferred bending zone that is located at the at least one joint,
• wherein the at least one joint is a single joint and wherein the first preferred-bending zone is an integral preferred-bending zone and the second preferred-bending zone is a jointed, non-integral preferred bending zone that is located at the single joint,
• wherein the first, integral preferred-bending zone comprises a first, integral hinge-pleat with an outward pleat tip and with an inward pleat valley that is flanked by first and second flanking inward pleat tips,
• wherein the first, integral hinge-pleat comprises first and second integral pleat-panels and wherein the first and second integral pleat-panels are non-separably bonded to each other in a bonding zone of each pleat-panel, so that the first, integral hinge-pleat is a bonded hinge-pleat,
• and
• wherein a non-integral tab is provided at the first, integral bonded hinge-pleat by way of being co-bonded to at least one of the first and second integral pleat-panels of the first, integral bonded hinge-pleat by the same bonding mechanism by which the first and second integral pleat-panels are bonded to each other to form the first, integral bonded hinge-pleat.