Rigid packaging
HDPE · PET · PP — bottles · jugs · jars · pails — neck finish + closure
Rigid packaging is bottles, jugs, jars, tubs and pails, plus the closures that go on them. The container and the closure are usually bought from different places, and a surprising amount of trouble comes from the point where they meet.
When I look at a rigid spec I look at three things first: the resin and gram weight, the neck finish, and how far the empty containers travel to get to you. Empty bottles are mostly air, and freight shows it.
Molded containers, and the closures that seal them.
Most rigid plastic packaging is made one of three ways. Extrusion blow molding makes HDPE bottles and jugs, including the ones with handles. Injection stretch blow molding makes clear PET bottles and jars. Injection molding makes closures, tubs and pails. Thermoformed trays and clamshells, glass, and metal containers round out the category.
The resin is picked for the product: HDPE for chemical resistance and toughness, PET for clarity, PP for heat resistance and closures, LDPE for squeezability.
Use it when
- The product is liquid, paste or loose and needs a container that holds its shape.
- You need a reclosable, pourable or dispensing package.
- The product needs stacking strength or protection a flexible package can't give.
- Shelf presence calls for a clear or shaped container.
What goes on a bottle and closure spec.
- Resin
- HDPE (jugs, chemical and household bottles, pails), PET (clear beverage, food and personal-care bottles and jars), PP (closures, tubs, hot-fill and microwave containers), LDPE (squeeze bottles). Also virgin vs. post-consumer recycled (PCR) content and color.
- Capacity
- Nominal fill volume and brimful (overflow) capacity. The difference is the headspace, and both belong on the spec.
- Gram weight
- The weight of plastic in each container. It drives material cost and affects top-load strength, drop performance and how the container handles on the line.
- Neck finish
- Written like 38-400: the first number is the nominal diameter in millimeters, the second is the finish style, which sets the thread height and number of turns (400, 410 and 415 are common). The closure must match the finish exactly.
- Closure
- Continuous-thread screw cap, child-resistant, tamper-evident band, flip-top or disc-top dispensing, pumps, triggers. Closure liner type — induction seal, foam, pulp/poly — decides how well it seals.
- Dimensions and label panel
- Height, diameter or footprint, and the label panel size if the container will be labeled.
- Compatibility and performance
- Product compatibility (stress cracking, permeation, paneling), top-load requirements for stacking, hot-fill or other process conditions, and any food-contact or regulatory requirements.
What drives the cost of rigid packaging.
Resin and gram weight
Material is a large part of the price, and resin prices move. A lighter container with the same performance takes cost out of every unit.
Stock vs. custom mold
Stock containers use molds the supplier already owns. A custom shape needs custom molds — a substantial one-time investment that has to be justified by volume or brand value.
Closure complexity
A plain screw cap costs far less than a dispensing, child-resistant or pump closure.
Decoration
Labels, shrink sleeves, screen printing and colored resin each add cost.
Freight
Empty containers ship mostly air. Distance from the molder can be a large share of the delivered cost.
Volume
Machine setup and minimums mean small runs of custom or colored containers carry a premium.
Where rigid packaging budgets leak.
Freight on empty containers
Shipping empty bottles long distances is expensive per unit. A molder closer to your filling plant can win on delivered cost even at a higher unit price.
Custom molds that don't earn their keep
A custom shape can make sense for a flagship product. For a low-volume SKU, a stock container with a good label usually does the job.
Closure and finish mismatch
A cap from one supplier and a bottle from another, with slightly different finishes, can leak, back off or fail torque. Specify and test them as a pair.
Heavier than necessary
Gram weights often stay where they were set years ago. Lightweighting needs testing for top-load and drop performance, but can pay off on every unit.
Pallet patterns for empties
How many empty containers fit on a pallet and a truck drives freight cost. Ask how they're packed — bulk, tiered or cased.
Questions buyers ask me about bottles, jars and closures.
What does 38-400 mean on a bottle?
It's the neck finish. 38 is the nominal diameter of the opening in millimeters, and 400 is the finish style, which defines the thread profile and height. A closure must match both numbers — a 38-400 cap is not interchangeable with a 38-410 bottle.
Should I use HDPE or PET?
PET is clear and stiff, and widely used for beverages, food and personal care. HDPE is opaque or translucent, tough and chemically resistant, and widely used for jugs, household chemicals and industrial products. Product compatibility, appearance and process conditions decide it.
Stock bottle or custom bottle?
Stock containers are faster and avoid mold costs, and there are a lot of them to choose from. Custom molds make sense when the shape is part of the brand or a functional requirement, and when volume justifies the tooling.
What's an induction seal?
It's a foil-laminated liner in the cap that gets heat-sealed to the bottle's rim by an induction sealer after capping. It gives a hermetic, tamper-evident seal that the consumer peels off.
Send me your rigid packaging spec.
Send me the bottle, the cap and where they get filled. I'll check the finish match and the freight before I talk about unit price.
Helpful to include
- Product and fill volume
- Container type, resin and neck finish, or a sample
- Closure type and liner
- Filling and capping equipment
- Decoration (label, sleeve, print)
- Annual volume and fill location
Related tools
For empty containers, cube and freight usually matter more than anything else.