RF welding, or radio-frequency welding, seals PVC and some TPU dry bag seams by heating the material from the inside with high-frequency energy. It produces a strong, airtight weld with no needle holes.
People searching for "rf welding" usually want a direct, practical answer - and this page delivers one. This guide explains the RF welding materials and construction methods that determine waterproofing, weight, durability and cost, so you can choose the right film and seam for your use case.
How RF welding works
High-frequency radio waves excite the molecules in the film, generating heat exactly at the joint. Pressure fuses the layers into a single welded seam.
Where it is used
RF welding is the standard for PVC dry bags and works on many TPU films. It is fast, consistent and produces seams that are as waterproof as the material itself.
Why it beats stitching
Stitching punctures fabric and needs taping, while an RF weld fuses the material so there is no hole to leak. The result is stronger and fully watertight.
Why seams matter more than fabric
A RF welding leaks at the seam or closure far more often than through the film. That is why factories spend so much effort on welding quality and closure hardware, and why stitched bags must be seam-taped.
When evaluating a supplier, ask about the welding method and the seam test. A smooth RF weld with documented seam-strength testing is a strong signal that the bag will hold water out.
Cold weather behavior
PVC stiffens in cold, which makes a RF welding harder to roll and close in winter conditions. TPU stays flexible down to lower temperatures, which is why it is preferred for skiing, alpine and cold-water use.
If you paddle or travel in cold climates, choose TPU or a TPU-coated nylon. If the bag will live in a warm climate or a boat locker, PVC's stiffness is less of a problem.
How the material affects weight
Weight scales with the film. Coated nylon is lightest, TPU is mid-weight, and PVC is heaviest. For backpackers and travelers, saving grams matters; for a boat or car-based trip, heavier PVC durability is less of a burden.
A RF welding spec sheet usually lists the film thickness in mil or mm plus the finished weight. Thinner film is lighter but less puncture-resistant, so match thickness to the abuse the bag will face.
Welding: how seams are made
A RF welding seam is usually made by RF (radio frequency) or high-frequency welding, which fuses PVC or TPU film into one continuous layer using electromagnetic energy. Heat sealing is used for thinner films and simpler layouts.
Coated nylon cannot always be welded, so its seams are stitched and then covered with waterproof seam tape. A well-welded seam is smooth, even and free of bubbles, and it should be as strong as the film itself.
Denier and film thickness
A RF welding spec lists film thickness in mil or mm and, for coated fabrics, denier for the base weave. Higher denier means a heavier, tougher base fabric, while thicker film adds puncture resistance and weight.
Match the numbers to the abuse: a thin, light film suits packable travel bags, while a thicker film or higher denier suits river and expedition use.
TPU, PVC and coated nylon compared
TPU (thermoplastic polyurethane) is a flexible, weldable film that stays soft in cold weather and resists UV better than PVC. It is the premium choice for lightweight, high-performance dry bags.
PVC (polyvinyl chloride) is tougher and cheaper but heavier, and it stiffens below freezing. Coated nylon uses woven nylon with a waterproof coating or laminate, giving the lightest and most packable fabric.
| Aspect | Detail |
|---|---|
| Material | PVC, some TPU |
| Seam | Airtight |
| Speed | Fast |
| Material | Waterproofing | Weight | Durability | Cold / UV | Cost |
|---|---|---|---|---|---|
| TPU | Excellent, weldable | Light | Good | Best UV, soft in cold | Higher |
| PVC | Excellent, weldable | Heavier | Very high | Stiffens in cold, moderate UV | Lowest |
| Coated nylon | Good (depends on coating) | Lightest | Good | Moderate | Medium |
| Method | How it works | Best for |
|---|---|---|
| RF / high-frequency | Fuses film with electromagnetic energy | PVC and TPU seams |
| Heat sealing | Heated bar melts film together | Thinner films, simple seams |
| Seam taping | Waterproof tape over stitched seams | Coated nylon fabrics |
| Priority | Best material |
|---|---|
| Lightest weight | Coated nylon |
| Lowest cost | PVC |
| Cold weather | TPU |
| Puncture resistance | Thick PVC |
| UV exposure | TPU |
| Thickness | Typical use |
|---|---|
| 0.3-0.5mm | Light travel bags |
| 0.5-0.7mm | Everyday dry bags |
| 0.7mm+ | Expedition and river bags |
How rf welding actually works
Radio-frequency (rf) welding, also called high-frequency (HF) welding, uses a 27.12 MHz electromagnetic field to excite polar polymer molecules in PVC and TPU, generating heat from within the material rather than from a hot die. The film is placed between a copper electrode and a ground platen, pressure is applied, and the material fuses in 1.5 to 3 seconds without melting through.
The result is a seam as strong as the film itself, clean and flat, and fully waterproof. Stitched seams with seam tape are a backup; rf-welded seams are the gold standard for TPU and PVC dry bags because there is no needle hole to leak.
Machine parameters that control quality
A typical rf weld on 0.5 mm TPU uses 2 to 4 kW of power, 0.3 to 0.5 MPa electrode pressure, and a 1.5 to 2.5 second dwell, followed by a 1-second cool-down under pressure so the seam does not creep. On 0.7 mm PVC, dwell extends to 2.5 to 3.5 seconds. Too short and the seam peels; too long and the film foams and embrittles.
The electrode must be the exact seam width (usually 20 to 25 mm) and wrapped in PTFE tape to prevent sticking. A well-tuned line welds about 600 to 1,200 seams per shift. QUANZHOU JUNYUAN BAGS runs 149 welding and cutting machines across 7 production lines, with each operator logging the rf parameters per lot so the same bag repeats identically on reorder.
What can and cannot be rf welded
Rf welding works on PVC and TPU, and on PU-coated fabrics with a TPU lamination layer. It does not work on pure silicone, polypropylene or polyethylene fabrics - those need hot-air tape or solvent cement. If a supplier offers rf welding on a silicone dry bag, they are either taping it or mislabeling the process.
Common rf welding defects
The three defects are cold welds (under-energy, peels by hand), burn-through (over-energy, foams the edge), and inconsistency (electrode drift, one side of the seam weak). A trained operator inspects every seam visually and pulls one sample per hour. If a factory cannot show you its in-line reject log, walk away.
Rf welding machine capacity
A standard 2 kW rf welder handles 0.35 to 0.5 mm TPU and PVC. A 5 kW welder handles 0.7 to 1.0 mm PVC for expedition bags. If a factory only has 2 kW machines, they cannot reliably weld 0.7 mm PVC - ask to see the machine nameplate. A 149-machine shop with a mix of 2 kW and 5 kW lines can run the full thickness range.
Setting up a weld QC line
A working rf-weld QC line has three stations: visual (operator inspects every seam for cold spots and burn-through), pull test (one sample per hour pulled to failure on a tensile tester, logged), and inflate/submerge (every bag inflated to 3 kPa and dipped in a tank for 10 seconds). That three-step process catches 99 percent of leaks before packing.
The cost of the in-line test is about 10 seconds per bag - negligible against a $30 to $80 retail price. A factory that skips the submerge step saves $0.50 per bag but ships 2 to 5 percent defective. At AQL 2.5 inspection, those defectives get rejected at the buyer's warehouse. The in-line test is cheaper than the rejection.
Rf welder capacity by machine
A 2 kW rf welder handles 0.35 to 0.5 mm TPU and PVC at about 600 to 1,200 seams per shift. A 5 kW welder handles 0.7 to 1.0 mm PVC for expedition bags. If a factory only has 2 kW machines, they cannot reliably weld 0.7 mm PVC - ask to see the machine nameplate. A shop with 149 machines across 7 lines can mix thicknesses on the same die.
The electrode is a precision copper die cut to the seam shape. Custom electrodes cost $300 to $800 and last about 50,000 cycles. Standard straight seams use a generic bar; shaped corners use a custom die.
Welding cost per bag
Rf welding labor is about $1.00 to $1.80 per bag, depending on seam length and complexity. A simple 20 L roll-top has about 1.5 meters of weld; a camera backpack with dividers has 4 to 5 meters. The machine and electrode amortize at 50,000 cycles. Complex weld geometry adds 20 to 40 percent to labor.
Ask the factory how many meters of weld per bag and how long a seam takes. A line that welds 800 bags per shift is efficient; one that welds 300 is not.
Electrode maintenance
Rf electrodes wear out after 50,000 cycles and need reconditioning. The PTFE tape covering the electrode must be replaced weekly to prevent film sticking. A well-maintained electrode produces a clean, uniform weld; a worn one produces cold spots. Ask the factory how often they recondition electrodes - weekly is the standard.
RF welding parameters
Radio-frequency welding works on PVC and polar TPU at 27.12 MHz, using a copper die shaped to the seam. The machine power is 3 to 8 kW, the die pressure is 2 to 4 bar, and the weld time is 2 to 5 seconds per 100 mm of seam. The die heats the film from the inside out, fusing the molecules without a needle. A good RF weld bead is 10 to 15 mm wide and peels at 30 to 50 N per 25 mm. Cold welds look shiny but separate; hot welds show a uniform melt pattern.
For QC, the weld temperature, pressure and time are logged per batch on a paper or digital chart. A weak batch traces to a dirty die, a misaligned die, or film that is too cold. Reject any seam where the weld bead is under 8 mm or where fingernail peeling lifts the film. At MOQ 1,000, RF welding labour is about USD 0.8 to 1.2 per 20 L bag. Hot-air welding is the alternative for non-polar TPU, at lower equipment cost but slightly lower peel strength.
People also ask
How do I clean a dry bag?
Rinse with fresh water, wipe with mild soap, and air-dry fully before storing. Avoid harsh solvents and keep zipper tracks clean of sand.
How are dry bags made?
The body is cut from waterproof film or coated fabric, seams are welded or taped, hardware is attached, and each bag is leak-tested before shipping.
Which dry bag material lasts longest?
PVC lasts longest under hard abrasion but stiffens; TPU stays flexible longer; nylon is lightest but the coating can wear. Storage and care matter as much as material.
What is the difference between waterproof and water resistant?
Waterproof means it keeps water out under submersion or jets; water resistant means it resists light rain and splashes but will leak under pressure or immersion.
Do TPU dry bags crack in the sun?
TPU has better UV resistance than PVC, but prolonged direct sun still ages any film. Store dry bags out of direct sunlight when not in use.
Do PVC dry bags get stiff in the cold?
Yes. PVC stiffens below freezing, which can make rolling and closing harder. TPU stays flexible in cold conditions.
What does IPX8 mean on a dry bag?
IPX8 means the bag survives continuous immersion beyond 1 meter under manufacturer-specified conditions. The depth and duration are only meaningful if stated.
What is the difference between TPU and PVC dry bags?
TPU is lighter, softer and more UV-stable; PVC is heavier, more puncture-resistant and cheaper. TPU suits premium packable bags; PVC suits rugged, high-volume bags.
Key takeaways
- Choose RF welding by fixing the activity, size, material and closure before comparing options.
- Verify waterproofing with a stated IPX rating and a real test method, not a label.
- For bulk orders, confirm MOQ, lead time and a pre-production sample before committing.
- Match material to conditions: TPU for cold and UV, PVC for abrasion, coated nylon for weight.
- A physical pre-production sample is the only reliable way to lock material, color and printing.
- Store dry bags loose and shaded, and re-test the seal before trusting them with electronics.
Related guides
- What is a dry bag?
- Dry bag materials: TPU vs PVC vs nylon
- IPX / IP68 waterproof ratings
- Types of dry bags
- OEM dry bags
Step by step
- Decide your priority: weight, cost, cold performance or puncture resistance.
- Choose TPU, PVC or coated nylon accordingly.
- Check the seam method - welded or seam-taped - and the film thickness.
- Confirm any compliance needs such as REACH, RoHS or food-grade material.
Specification checklist
- Fix the specification first - material, size, closure, printing and packaging - so quotes are comparable.
- Verify waterproofing with a stated IPX rating and a real test method, and confirm the batch sampling plan.
- Order a pre-production sample and approve it before bulk production begins.
- Confirm MOQ, lead time, payment terms and the correct HS code before you commit.
- Match the material to the conditions: TPU for cold and UV, PVC for abrasion, coated nylon for weight.
- Ask for a dated test report and a pre-shipment inspection (AQL) for waterproofing and seams.
- Keep the most valuable items in an inner pouch as a second layer of protection.
- Rinse, dry and store the bag correctly to extend its lifespan season after season.
Bottom line
The bottom line is that material choice is a trade-off, not a ranking. TPU is the premium all-rounder, PVC is the tough budget workhorse, and coated nylon is the light packable option. Pair the right film with welded or taped seams and the bag will perform as promised. For "rf welding", this is the summary that matters most.
Frequently Asked Questions
Q1. How do I clean a dry bag?
Rinse with fresh water, wipe with mild soap, and air-dry fully before storing. Avoid harsh solvents and keep zipper tracks clean of sand.
Q2. How are dry bags made?
The body is cut from waterproof film or coated fabric, seams are welded or taped, hardware is attached, and each bag is leak-tested before shipping.
Q3. Which dry bag material lasts longest?
PVC lasts longest under hard abrasion but stiffens; TPU stays flexible longer; nylon is lightest but the coating can wear. Storage and care matter as much as material.
Q4. What is the difference between waterproof and water resistant?
Waterproof means it keeps water out under submersion or jets; water resistant means it resists light rain and splashes but will leak under pressure or immersion.
Q5. Do TPU dry bags crack in the sun?
TPU has better UV resistance than PVC, but prolonged direct sun still ages any film. Store dry bags out of direct sunlight when not in use.
Q6. Do PVC dry bags get stiff in the cold?
Yes. PVC stiffens below freezing, which can make rolling and closing harder. TPU stays flexible in cold conditions.
Q7. What does IPX8 mean on a dry bag?
IPX8 means the bag survives continuous immersion beyond 1 meter under manufacturer-specified conditions. The depth and duration are only meaningful if stated.
Q8. What is the difference between TPU and PVC dry bags?
TPU is lighter, softer and more UV-stable; PVC is heavier, more puncture-resistant and cheaper. TPU suits premium packable bags; PVC suits rugged, high-volume bags.
Q9. How long do dry bags last?
A well-maintained dry bag lasts many seasons. PVC lasts longest in hard use but stiffens in cold; TPU stays flexible but is softer.
Q10. Does dry bag material affect waterproofing?
The material supplies the waterproof barrier, but the closure and seams decide real-world waterproofing. A good film still leaks if seams or closures fail.
Q11. What is seam taping?
Seam taping covers stitched seams with a waterproof tape to stop needle holes leaking. It is used on coated fabrics that cannot be welded.
Q12. Can you put a phone in a dry bag?
Yes, using a dedicated phone dry bag or a padded roll-top bag. Test the bag first and add padding for impact protection.
Q13. What is the difference between IP67 and IP68?
IP67 survives 30 minutes at 1 meter. IP68 survives beyond 1 meter or longer immersion, but the exact depth and time depend on the manufacturer's spec.
Q14. How do I fold a dry bag for storage?
Lay it flat, fold it loosely, and roll gently without creasing the film. Do not store it tightly rolled, which can crack the material.
Q15. What is the difference between IP68 and IPX8?
IP68 includes dust protection (6); IPX8 has no dust rating (X). For water protection the 8 is the same class of test.
Q16. What is the best material for a phone dry bag?
Clear TPU or PVC film is best for phone dry bags because it is transparent, touchscreen-friendly and seals well in a clamp closure.
Q17. How can I tell if a seam is well welded?
A good weld is smooth, even and free of gaps or bubbles. Pull gently along the seam - a strong weld should not peel or open.
Q18. How do I clean a dry bag?
Rinse with fresh water, wipe with mild soap and a soft cloth, and air-dry fully before storing. Avoid harsh solvents and high heat.
Q19. How do I fix a dry bag seam?
Use seam tape or liquid seam sealer made for TPU or PVC, apply it over the damaged weld, and let it cure fully before use.
Q20. Can a dry bag have an IP68 rating?
Yes, if tested to IP68 conditions. Confirm the exact test depth and duration, since IP68 alone does not guarantee a specific depth.