If you are learning how to choose a spout cap for a stand-up pouch or doypack, you will find no shortage of catalog pages listing diameters and materials. What most of them do not give you is a decision order: which specification to fix first, which numbers actually matter, and which ones you can safely leave to the supplier. This guide is that order. It walks the three decisions that decide whether your pouch works on the line and on the shelf — diameter, sealing temperature and material — and ends with a five-point checklist you can send to a supplier as an RFQ.
The frame matters before the details. Everything below is about spout caps for stand-up pouches and doypacks: the resealable plastic fitments heat-sealed into flexible beverage, sauce and liquid-food pouches. If you are looking for a gas-can spout or a kitchen faucet spout, this is not the guide you want.
The three decisions are not independent. Diameter decides how fast the product pours and how cleanly it doses. Sealing temperature decides whether the fitment survives being welded into your film. Material decides both of those, plus whether the finished pack clears food-contact compliance. Fix them in that order and you end up with a specification, not a part number. This article is part of our choosing and running spout caps series for buyers and pouch converters.
How to choose a spout cap for a stand-up pouch: three decisions, one order
Most buying mistakes start the same way: with the catalog. "What sizes do you have?" is the wrong first question, because a spout cap only works as part of a system — the product inside, the film around it, and the line that fills and seals it. Industry bodies such as the Flexible Packaging Association stress the same point about flexible packaging generally: components have to be engineered together, not picked separately.
Three inputs fix everything downstream:
- The product — viscosity, particles, fill temperature, and how much the end user should get per squeeze or pour.
- The pouch film — its sealant layer, and whether it is a conventional multi-layer structure or a recyclable mono-material PE film.
- The line — the heat-seal temperature, dwell time and pressure your sealer runs at, plus the capping equipment for the closure.
If you can answer those three, the selection becomes a lookup instead of a negotiation. If you cannot, a supplier's sample recommendation is a guess, however confident it sounds.
Step 1: Match the spout bore to what your pouch actually flows
The bore — the hole the product passes through — is a flow decision before it is a dimensional one. A bore too generous makes a thin liquid glug out faster than the user expects. A bore too narrow turns a thick purée into a pouch the customer reads as defective. Start with the product's viscosity and any particles in it, then pick the band that matches.
Bore range | What it handles well | Typical pouches |
|---|---|---|
1.2–6 mm | Controlled dosing of thin, low-particulate liquids | Cosmetics, essential oils, pharma samples |
7–13 mm | Everyday liquid foods at a comfortable pour | Juice, yogurt drinks, sauces, baby food |
14–22 mm | High-flow viscous and oil-based products | Ketchup, cooking oil, detergent, sports drinks |
26–40 mm | Bulk pouring and granular contents | Pet food, rice, grains, large refill pouches |
Within those bands, three sizes dominate the food and beverage market because filling lines are already tooled for them: 8.6 mm, 10 mm and 22 mm. Choosing one of the band sizes is the cheapest decision you can make — it rarely requires anything new on your side. If your product needs something between bands, that is where custom tooling starts, and it deserves a separate budget discussion.
One measurement trap: the "diameter" on a datasheet can mean the bore, the outer thread diameter, or the flange width, and they are three different numbers. For flow, ask for the bore or inner diameter. For sealing, you care about the flange, which is wider than both. When you ask a supplier for a dimension, name the feature you mean — bore, thread, or flange — or you will compare apples with pears across quotes. Our full diameter guide walks each band bore by bore with model examples.
The bore is the flow dimension; the flange is the sealing dimension. Ask for both.
If your product contains particles larger than about 2 mm — chilli flakes, fruit pieces, granular seasonings — treat the bore as a particle-size filter first. A fitment that pours liquid beautifully will clog on the first use, which reads as a product defect, not a packaging one. And if the product settles or needs to be drained to the last dose — cosmetics, essential oils, thick sauces — ask whether the spout family offers a dip tube with adjustable length, so the end user reaches the bottom of the pouch instead of tipping it.
Step 2: Sealing temperature — the window your spout and your pouch film have to share
Sealing is where most spout caps actually fail, and it is the step every catalog skips. A spout has to survive two different thermal events, and they pull in opposite directions:
- Sealing temperature — the moment the flange is welded into the pouch film. It happens once, hot, for a fraction of a second.
- Process resistance — retort, hot-fill or pasteurisation, where the finished pack sits at temperature for minutes.
Those are two different numbers. Ask for both, because a spout can seal beautifully and still creep out of round in a retort.
The numbers that matter in practice: 110–130 °C is the low-temperature sealing window that lets a spout weld into recyclable mono-material PE pouches without distorting, and 121 °C is the retort rating that sterilisation cycles run at. Too cold and you get an incomplete weld — the classic leak that appears after filling, not during. Too hot and the neck or thread deforms just enough that the cap no longer torques down evenly.
The seal itself is a shared window between two materials: your film's sealant layer and the spout's flange resin. The film supplier can tell you the sealant's activation temperature; the spout supplier must confirm their flange fuses inside that window. If the two numbers do not overlap, no amount of line tweaking fully fixes it. Ask also which sealing head and parameters the flange was validated with — temperature, dwell and pressure — and whether a spout sealing machine is part of the recommended setup. Heatsealability is testable in a standardised way, for example under ASTM F2029, so you can ask for test data instead of assurances.
If you are moving to recyclable mono-material PE film — and many brands are — low-temperature sealing is not optional. Standard PP spouts need a hotter window than the film can take. Our guide to spout cap sealing temperature covers the film side of this trade-off in depth.
The flange weld is the single most common failure point — the window has to fit your film's sealant layer.
Step 3: Pouch spout materials — PE, PP and the food-contact rules that decide
Once the diameter and the temperature window are fixed, the material choice is mostly resolved — but it is worth knowing why, because it also settles your compliance paperwork.
Property | PE (polyethylene) | PP (polypropylene) |
|---|---|---|
Sealing temperature | Lower — suits low-temperature and mono-material lines | Higher |
Stiffness and thread integrity | Softer, more flexible | Stiffer — better torque retention |
Chemical resistance | Good | Better for oils and aggressive fillings |
Retort capability | Limited | Up to 121 °C retort |
Recyclability context | Fits mono-material PE pouches | Mixed-stream recycling |
For food, beverage, cosmetic and pharmaceutical pouches, the resin must be food-grade virgin material — no recycled content, no brighteners or fluorescers that can migrate into the product. A supplier should be able to name the resin brand and grade, not just say "food-grade".
The compliance path is where most supplier claims get vague, and it has a fixed structure you can check yourself:
- US market: food-contact polymers are regulated by FDA's olefin polymer rule, 21 CFR 177.1520, with the general framework explained in FDA's food ingredients and packaging resources.
- EU market: the framework is Regulation (EC) 1935/2004 on food-contact materials, and for plastic parts specifically, Regulation (EU) 10/2011 on migration from plastic food-contact materials.
- China: GB 4806.7 covers food-contact plastic materials and articles, and is commonly cited on product specs alongside the EU and US references.
Ask for three documents, in this order: the certificate (FDA registration or EU 1935/2004 declaration), the migration test report covering your filling type, and the resin grade certificate. A supplier who hesitates on any of the three is telling you something. What food-grade certification actually covers is worth a read before you compare certificates, because the wording on them varies.
For reference, Ruihua molds its food-contact spout caps from virgin PP and PE without brighteners or fluorescers, and carries an EU 1935/2004 certificate issued under TÜV SÜD verification plus FDA food-contact compliance per 21 CFR 177.1520, with GB 4806.7 cited on food-contact models — the same three documents we recommend you request from any supplier.
Food-contact compliance starts with the resin: virgin grade, no brighteners, and certificates you can verify.
Step 4: Closure style, torque and tamper evidence for pouch spouts
The closure is the part the end user touches, so its design follows the use case more than the chemistry:
- Screw caps — the standard for resealable food pouches; best torque control and leak performance.
- Flip-top and push-pull closures — one-hand dispensing for sports drinks, sauces and household chemicals.
- Child-resistant and anti-choking designs — for household chemicals and pharma-adjacent products where regulation or safety practice demands them.
- Long-nozzle spouts — for precise, narrow pours into small openings.
Two specifications matter on every closure. Torque: the cap–neck interface is designed around a torque range — too low leaks in transit, too high is hard for the user. Ask for the recommended torque and the leak-test method behind it. Tamper evidence: a pilfer-proof ring is expected in most food and beverage markets, and in the EU, cap design is now additionally constrained by the tethered-cap requirements under the Single-Use Plastics Directive — worth checking before you lock a design, because EU tethered-cap rules apply to pouches too.
Finally, the closure has to run on your line: capping heads and spindle sizes differ between suppliers, and a cap that is perfect on paper but needs a new capper is a budget surprise. Mention your filling and capping equipment in the enquiry. You can browse the spout cap range to see how closure types map to diameters in practice.
Step 5: The five-point RFQ checklist for pouch spout suppliers
Send this with your next enquiry, and you will get comparable quotes instead of marketing:
- Product and flow — viscosity, particle size, fill temperature, target dose per use.
- Diameter — bore, thread and flange dimensions you need, or the band from Step 1 if you want the supplier to propose.
- Sealing and process — your film structure (including mono-material PE), sealant activation temperature, sealer settings, and whether retort or hot-fill applies.
- Material and compliance — resin grade required, target markets (US/EU/China), and the three documents from Step 3.
- Closure and logistics — cap style, torque range, tamper evidence, capping equipment, plus MOQ, sampling rounds and lead time.
A supplier that answers all five points in one reply, with numbers and documents, is a shortlist candidate. One that answers with "we have many options" is not. Ruihua's range covers 117 spout-cap SKUs from 1.2 to 40 mm including low-temperature-sealing and retort-rated series, so the checklist above is the exact format our engineers work from.
The checklist turns a selection exercise into a supplier test — comparable quotes, not marketing.
FAQ
What is the difference between a spout cap and a fitment?
In flexible packaging the words are often used interchangeably. Strictly, the fitment is the whole plastic assembly heat-sealed into the pouch — flange, spout body and closure together — while "spout cap" usually means the visible spout with its cap. When you order, use "pouch fitment" or "spout cap for stand-up pouch" and specify which parts you need, because some suppliers sell the spout and cap separately.
How do I know which diameter I need?
Measure the flow, not the shelf. For thin liquids with no particles, an 8.6 mm or 10 mm bore covers most food and beverage pouches. For viscous products like ketchup or oil, go to 14–22 mm. For bulk or granular contents, 26–40 mm. If the pouch is already tooled for a filling line, ask the line builder which bore it was set up for — that is usually the cheapest answer.
Are spout caps recyclable?
It depends on the resin and the pouch. The trend that matters is mono-material PE pouches: if your film is all-PE, the spout must also be a low-temperature-sealing PE-compatible part that welds into it and can go through PE recycling streams. PP spouts in a mono-material PE pouch break the recyclability of the pack. Ask your supplier for their low-temperature sealing range before committing to an all-PE structure.
How do I verify food-grade claims?
Ask for the certificate, the migration test report and the resin grade — in that order — and check the certificate against the issuing body. FDA food-contact compliance for olefin polymers follows 21 CFR 177.1520; EU compliance follows Regulation (EC) 1935/2004 with migration testing under Regulation (EU) 10/2011. A supplier that cannot produce the resin grade or the migration report is not food-grade certified in any practical sense.
If this is the first time you are specifying a spout cap for a pouch, the order above — product, film and line first; then diameter, sealing, material, closure; then the RFQ — will get you a specification a supplier can actually build to. Send the checklist to our technical team for a free review, and request samples of the diameter and material you shortlist; sample testing on your own line beats any datasheet.
