What Is a Kynar Gas Sampling Bag Used For? A Guide from Analytical Specialties
A Kynar gas sampling bag is a bag made from PVDF film that labs use to collect and hold air or gas samples for analysis. Analytical Specialties makes 3 mil Kynar bags for ambient emission sampling and 4 mil bags, preconditioned for low background, for automotive emission testing (Kynar Gas Sampling Bags).
If you work in an emission testing lab, you already know the bag can spoil a result before the sample ever reaches the instrument. Film that gives off its own compounds shows up in the data. That is the problem Kynar film was brought in to solve. This guide covers what the material is, why it was developed, how the two thicknesses differ, and which size to order.
What is Kynar (PVDF) material?
Kynar is a trade name for polyvinylidene difluoride, or PVDF. On its Kynar gas sampling bags page, Analytical Specialties describes PVDF as a highly non-reactive, pure thermoplastic fluoropolymer. For a sampling bag, that matters because the film should hold the gas without reacting with it. The PVDF resin is sold under the Kynar name by Arkema, and the film used in Analytical Specialties bags is made by Westlake Plastics from Kynar PVDF.
Analytical Specialties lists these advantages of the film:
- Excellent chemical resistance
- Stable to UV and the effects of weather
- Excellent transmittance of solar energy
- High heat resistance
- Superior physical and mechanical properties
- FDA compliant resin
Buyers often ask how well the film holds specific gases. The permeability figures below are from the Analytical Specialties PVDF gas permeability data, based on 100 micron film thickness at 23°C over 24 hours. Testing follows ASTM D1434 for gases and DIN 53122 for water vapor.
| Permeant | Rate (100 µm film, 23°C, 24 h) |
|---|---|
| Water vapor | 2.0 g/m² per 24 h at STP |
| Air | 7.0 cc/m² per 24 h at STP |
| Oxygen | 20.0 cc/m² per 24 h at STP |
| Nitrogen | 30.0 cc/m² per 24 h at STP |
| Carbon dioxide | 60.0 cc/m² per 24 h at STP |
The full permeability sheet can be sent to buyers on request.
Why was Kynar film developed for gas sampling bags?
According to Analytical Specialties, Kynar film was developed because the automotive industry needed a cleaner bag than Tedlar could give. Tedlar was the film specified in the Federal Register, but emission testing labs were moving toward much lower detection levels.
The company's account goes like this. Tedlar's manufacturing component, DMAC, stayed in the film. It could outgas hydrocarbons and, in some cases, cause analytical test failures. Then came LEV and ULEV vehicles. Testing those cars meant film contamination had to be measured in parts per billion instead of parts per million, which was the range current films were working in. So the need was simple: a film that adds as little as possible to the sample.
What is the difference between 3 mil and 4 mil Kynar bags?
The 3 mil bag is for ambient emission sampling and is priced close to Tedlar. The 4 mil bag is for automotive emission sampling. It is preconditioned with special bakes and handling so that background levels land between 45 and 65 parts per billion. This preconditioning is what reduces the film's own hydrocarbons to the low parts-per-billion range.
Think of it as a choice between everyday sampling and low background work. If you sample ambient air and want a fluoropolymer bag at a price close to what you pay for Tedlar, the 3 mil film is the usual fit. If your lab runs vehicle emission tests, such as SHED tests, where the bag's own background has to stay in the parts per billion range, the 4 mil preconditioned bag is the one built for that job. If you are not sure which thickness suits your method, the sales team can talk it through before you order.
What are Kynar gas sampling bags used for?
Kynar gas sampling bags are used for two main jobs: automotive emission testing, where the 4 mil preconditioned bag keeps background low, and ambient emission sampling, where the 3 mil bag gives fluoropolymer performance at a price close to Tedlar.
Automotive emission testing. This is where the film started. Labs testing LEV and ULEV vehicles, and running SHED tests, need a bag whose own contamination sits in the parts per billion range, so the reading reflects the exhaust and not the container.
Ambient emission sampling. Air quality and emission sampling work outside the vehicle lab also uses Kynar. Here the 3 mil film is the common choice for automotive emission testing and other low hydrocarbon analysis.
Every standard bag ships with a Jaco 1/4" nylon fitting installed in the center of the bag unless you ask for something else. Any other fitting needed to meet your application can be fitted; contact Analytical Specialties for pricing. If your setup needs a different connection, see the fittings for sampling bags page.
How does Kynar compare with Tedlar for gas sampling?
The short answer from Analytical Specialties: Kynar was developed for labs that need lower background than Tedlar provides, because DMAC left in Tedlar film can outgas hydrocarbons. The 3 mil Kynar bag is priced close to Tedlar, so cost is not always the deciding factor.
In practice, Analytical Specialties does not usually steer a buyer away from Kynar toward Tedlar. Tedlar is still the film many methods name, and Analytical Specialties makes Tedlar sampling bags too. The choice usually comes down to how low your lab needs the bag background to be and what your method calls for.
What sizes do Kynar sampling bags come in, and how much do they hold?
Analytical Specialties stocks eight standard Kynar bag sizes, from 6" x 6" to 24" x 24". Approximate volumes run from about 0.6 liters in the smallest bag to about 40 liters in the largest.
| Size | Catalogue number | Approximate volume |
|---|---|---|
| 6" x 6" | ASK5349 | 0.6 L |
| 7" x 7" | ASK5350 | 1 L |
| 9" x 9" | ASK5351 | 2 L |
| 10" x 10" | ASK5352 | 3 L |
| 12" x 12" | ASK5353 | 5 L |
| 12" x 18" | ASK5354 | 10 L |
| 18" x 18" | ASK5355 | 20 L |
| 24" x 24" | ASK5356 | 40 L |
Volumes are approximate. For current pricing and the $200 minimum order, see the Kynar Gas Sampling Bags product page. Analytical Specialties also builds Kynar bags custom to specification.
Frequently asked questions
Is Kynar the same as PVDF?
Yes. Kynar is a trade name for polyvinylidene difluoride, or PVDF. Analytical Specialties describes it as a highly non-reactive, pure thermoplastic fluoropolymer, which is why it is used for gas sampling bags.
Is Kynar better than Tedlar for gas sampling?
It depends on your method. According to Analytical Specialties, Kynar was developed for labs that need lower background than Tedlar, since DMAC left in Tedlar film can outgas hydrocarbons.
What is the background level of a 4 mil Kynar bag?
The 4 mil Kynar bag is preconditioned with special bakes and handling to reach background levels between 45 and 65 parts per billion. It is made for automotive emission sampling, including SHED tests.
What fitting comes on a Kynar sampling bag?
Standard Kynar bags come with a Jaco 1/4" nylon fitting installed in the center of the bag, unless you specify a different fitting when you order. Any fitting needed to meet the application requirement can be used; contact Analytical Specialties for pricing.
Is there a minimum order for Kynar bags?
Yes. The minimum order is $200. Current pricing for each size is listed on the Kynar Gas Sampling Bags product page.
Ready to order, or not sure which bag fits your method? See the Kynar Gas Sampling Bags page, use the online contact form, or call (630) 578-6731 or email sales@analyticalspecialties.com and the team will help you choose between 3 mil and 4 mil and the right size.
