polyethylene or polycarbonate by processes known in the art such as blowmolding or injection molding the bottle body is formed with a threaded lip 16 at its open end 12 so that a conventional elastomeric nipple 18 can be clamped against the top of the bottle by a threaded ring 20 which is screwed onto the threaded lip 16 of the bottle the partially closed end 14 of the bottle body is formed with a hole 22 for receiving a vent 23 the vent would be secured in the hole by one of the methods discussed below the vent 23 is made from macroporous plastic plastic herein is defined as one of a variety of hydrophobic thermoplastic polymers including high density polyethylene hdpe ultra high molecular weight polyethylene uhmw polypropylene pp polyvinylidene fluoride pvdf polytetrafluoroethylene ptfe nylon 6 n6 and polyethersulfone pes it is known to make macroporous plastic by a process called sintering wherein powdered or granular thermoplastic polymers are subjected to the action of heat and pressure to cause partial agglomeration of the granules and formation of a cohesive macroporous sheet the macroporous sheet is comprised of a network of interconnected macropores which form a tortuous path through the sheet typically the void volume of a macroporous sheet is from 30 to 65 depending on the conditions of sintering due to surface tension liquids cannot penetrate the small pores at the surface of the sheet but air can readily.