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Lids get lost. Caps get lost even more often, and on a straw cup the plug that seals the straw is the part most likely to disappear into a bag or a sink. The lid shown here solves that with a silicone tether: the sealing plug stays physically attached to the lid through a moulded silicone band, so it can be pulled off for drinking but never goes further than its leash allows.
Three views show the underside with the tether and plug, the lid on the cup with the plug pulled, and the side profile. The tether is soft silicone moulded as its own part and assembled between the plug and a retaining feature on the lid.
A flip cover on a hinge would solve the same problem, but a straw plug works differently: it pulls out axially, it needs a clear bore behind it while drinking, and it gets handled wet. A silicone tether gives that plug full freedom of movement, to swing, to park against any side of the cup, to stay out of the way while the user drinks, while remaining captive. A hinge that had to reach the same positions would need a geometry that fights all of them at once.
The tether material matters as much as the concept. Silicone takes the repeated stretching of daily use, keeps its elasticity through hot and cold drinks, and tolerates the washing cycle. A thermoplastic band of the same shape would stiffen, craze or tear off at the anchor within months.
The plug is a moulded cylinder sized to the straw bore with a defined interference, enough that it does not weep in a bag, light enough that it pulls one-handed. The seal is soft-on-rigid: the plug’s surface conforms to the bore rather than relying on perfectly matched hard surfaces, which is what keeps the claim honest after hundreds of cycles of pulling and re-seating.
The anchor points, where the tether meets the plug and the lid, are the failure points to design. Each end passes through a moulded retaining feature that clamps the silicone mechanically rather than gluing it, so the connection survives washing and pulling without relying on adhesion.
The lid body moulds in one piece, the plug in another, the tether in silicone in a third. That sounds like an assembly burden until you consider the alternative: overmoulding silicone in the same shot demands tools and cycle times that a replacement accessory rarely justifies. Moulding the parts separately and clipping the tether through its retainers keeps each part in its cheapest process and the assembly to one manual step.
Tether pull-off force at both anchors, sampled across the lot. Plug retention and re-seal after hundreds of cycles. Seal integrity on a filled cup, tipped and squeezed. Silicone compatibility with heat and dishwasher cycles, and colour match of the three parts against approved masters.
Kunshan Maifeng Precision Industry Co., Ltd. reviews drinkware closure designs before quoting, builds the injection molds in house, and molds single-color and dual-color parts on 36 machines from 90 to 700 tons. Send us the straw bore drawing and the tether requirement, and we will come back with a feasibility comment and a tooling proposal.
Kunshan Maifeng Precision Industry Co., Ltd. (MIF) has an investment of RMB 35 million and an independent factory of more than 5,000 m². The company operates 36 single- and dual-color injection molding machines from 90 to 700 tons, together with more than 50 sets of mold manufacturing and processing equipment. Our service, management and production team includes over 100 people.
Our parent company was established in 2008. We provide product design, mold design and manufacturing, injection molding and product assembly services for custom plastic parts, supporting both domestic and international customers.
1. Product Design
Product structure design and optimization based on customer drawings and samples.
2. Mold Design
Mold design developed around product geometry, material and production requirements.
3. Mold Manufacturing
Machining, polishing, fitting and assembly for custom injection molds.
4. Injection Molding
Single- and dual-color injection molding for project and order requirements.
5. Product Assembly
Supporting assembly services for molded plastic components.
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