Quick answer: Compostable trash bags are measured in microns, and most household kitchen bags range from 18 to 30 microns. Light dry waste works with thinner film; wet food scraps need more. Thickness is not the same as strength, so the seal, the resin blend, and the test data matter as much as the number on the spec sheet.
What Does Bag Thickness Actually Measure?
Bag thickness is a measure of the film wall, not the bag as a whole. Two units dominate the market, and they are not interchangeable.
Micron (µm) is one thousandth of a millimetre. A 20 micron bag has a film wall of 0.020 mm. Europe and most of Asia use this unit, and compostability standards and factory spec sheets are written in it.
Mil is one thousandth of an inch, so 1 mil equals 25.4 microns. This is the unit most North American buyers use in conversation and on retail packaging. The confusion starts when a bag described as “1 mil” turns out to be 25 microns on one supplier’s sheet and 22 microns on another, because both rounded.
Gauge is the third term you will meet. In flexible film, it usually means mil, but some suppliers use it loosely enough that it is worth confirming before you order.
Micron to mil conversion chart
| Micron (µm) | Mil | Millimetre | Typical use |
| 12 | 0.47 | 0.012 | Light dry waste, small bin liners |
| 15 | 0.59 | 0.015 | Dry waste, office bins |
| 18 | 0.71 | 0.018 | Household mixed waste, common baseline |
| 20 | 0.79 | 0.020 | Household kitchen waste |
| 25 | 0.98 | 0.025 | Wet food scraps, heavier loads |
| 30 | 1.18 | 0.030 | Sharp or heavy items, larger bins |
| 35 | 1.38 | 0.035 | Commercial and heavier-duty use |
To convert in your head, divide microns by 25.4 to get mil, or multiply mil by 25.4 to get microns.
Why the number on the box is not the whole story
A quoted thickness is a nominal figure, and film is manufactured within a tolerance rather than to an exact value. A bag listed at 20 microns may measure 19.2 in one area and 20.6 in another, and this variation is normal in blown film. Suppliers usually state a nominal number plus a tolerance band, commonly around plus or minus five percent, though this varies by factory and by line.
The practical consequence for buyers is simple. Comparing two quotes only works when both are quoted in the same unit, at the same measurement method, with the same tolerance band. A quote of “1 mil” and a quote of “25 micron” may describe the same film, or two films that differ by fifteen percent, and nothing on the quote tells you which.
Thickness is also measured at a point, not across the whole bag. A micrometer reading taken at the centre of the panel says little about the gusset, the seal line or the corner where the film stretches thinnest during forming. Buyers who need a defensible number ask for a measurement taken at several points across the bag and for the method used to take it.
Why Compostable Bags Need Different Thickness Than Plastic
Quick answer: Compostable film and polyethylene fail in different ways. PE stretches a long way before it breaks, so a thin PE bag can still carry a loaded bin. PLA is stiff, tears easily at thin gauges, and PBAT restores flexibility at lower strength. A compostable bag therefore usually needs a heavier gauge to reach the same load rating.
Where the strength difference comes from
Polyethylene is a long-chain polyolefin with high elongation and good tear resistance. A 15 micron LDPE liner will stretch around a sharp edge and hold, which is why thin PE bags survive loads that would split a compostable bag of the same gauge.
Polylactic acid behaves almost oppositely. It is stiff, clear, and high in tensile strength, but its elongation at break is low, so at thin gauges it cracks rather than stretches. On its own, it is a poor film for a bag that has to be pulled out of a bin.
PBAT is what makes the film usable. It is a flexible polyester with high elongation that acts as the softener in a PLA blend. The trade-off is that PBAT contributes flexibility rather than load-bearing strength, so the blend ratio decides where the finished film lands.
| Property, typical published range | LDPE film | PLA homopolymer | PBAT-rich compostable film |
| Tensile strength | 10–25 MPa | 50–70 MPa | 10–20 MPa |
| Elongation at break | 300–800% | 3–10% | 400–700% |
| Tear resistance | High | Low | High |
| Heat resistance | up to about 90–100 °C | limited by glass transition near 55–60 °C | softens below PE |
The middle column is the reason a compostable bag is not simply a thin PLA bag. PLA gives stiffness and strength but almost no stretch, so it is almost always blended with PBAT and often with starch before it becomes film. A finished compostable film therefore sits between the last two columns rather than at either extreme.
These are typical ranges for the material families, not a specification. Films differ by grade, blend ratio, and additive package, and the numbers on a supplier datasheet always outrank a table like this one.
Why the “15 to 25 percent thicker” rule is only a starting point
Suppliers and buyers often quote a rule of thumb that a compostable bag needs to be 15 to 25 percent heavier than the PE bag it replaces. The figure is a useful conversation starter and a poor engineering rule, because no published standard fixes it and the real gap depends on four variables that change from order to order.
The first is blend ratio. A formulation weighted towards PBAT is more flexible but carries less load per micron than one weighted towards PLA with a toughening additive. The second is bag construction. A star-seal base spreads load across more film than a flat seal and can carry the same weight at a lower gauge. The third is the load profile, since a light dry load and a wet food load pull on the seal in different ways. The fourth is the failure you are trying to prevent, whether that is a puncture from a bone or a seam split under a full bin.
A buyer who needs a number rather than a rule should test rather than calculate. Fill a sample to the intended working load, hang it for the expected residence time, and check the seal and the base rather than only the panel.
Why you cannot simply keep adding thickness
Thicker film is not automatically safer in a compostable programme, and this is where the material differs most sharply from PE. Three constraints cap how far you can go.
The certificate covers the finished article, not the resin. A compostability certificate is issued against a specific product at a specific construction, and it may state a gauge or weight range for the certified scope. Moving from a 20 micron unprinted film to a 25 micron printed bag can take the product outside the tested scope, which means the logo on the bag is no longer supported by the test report behind it. Print coverage and adhesives sit inside the same boundary, since the tests were run on the finished item.
Disintegration runs on a clock. EN 13432 requires at least 90 percent of the material to break down to fragments under 2 mm within 12 weeks, and 90 percent biodegradation within 6 months under industrial conditions. A heavier film has more polymer to break down in the same window, so thickness and formulation have to be developed together rather than thickness alone being pushed upward.
The processing window is narrower. Compostable polyesters need drying to a low moisture content before extrusion, and their melt strength and bubble stability differ from PE. A heavier gauge usually means a different temperature profile on the line. A gauge that runs cleanly in one season can fail in another when humidity changes, which is a production issue rather than a film property. On ShinHigh’s blown film lines in Dongguan, the season is written into the set-up sheet alongside resin moisture and ambient temperature, because a setting that holds in a dry week does not always hold in a humid one.
The practical question for a buyer is therefore not “how thick can I get” but “what is the thinnest gauge that carries my load inside the certified scope”. That question has a defensible answer, and it usually needs a sample rather than a datasheet.
With the material behaviour clear, the next step is matching a gauge to the waste the bag will actually hold.
Which Thickness for Which Waste Type?
Quick answer: Match the gauge to the load rather than to the bin. Dry light waste works at 15 to 18 microns, mixed household waste at 18 to 20, wet food scraps at 20 to 25, and sharp or heavy items at 25 to 30. Below 15 microns, compostable film is usually too thin for a bag that has to be lifted out full.
The short answer table
| What goes in the bag | Starting gauge | In mil | Why this range |
| Dry, light waste: paper, packaging, office and bathroom bins | 15–18 µm | 0.59–0.71 | Almost no weight and no liquid, so the film only has to resist tearing at the seal |
| Mixed household kitchen waste | 18–20 µm | 0.71–0.79 | The most common case, carrying a mix of wet and dry with moderate weight |
| Wet food scraps, high liquid content | 20–25 µm | 0.79–0.98 | Liquid adds load and softens the film, and the bag is usually carried while full |
| Sharp or heavy items: bones, shells, glass, broken crockery | 25–30 µm | 0.98–1.18 | Puncture resistance matters more than tensile strength here |
| Garden and yard waste | 25–30 µm | 0.98–1.18 | Twigs and prunings concentrate force on a small area and need film that resists a point load |
Two habits make this table work in practice. Weigh the full bag once before ordering, since most buyers overestimate how heavy a kitchen bin actually gets. And treat the ranges as starting points rather than fixed grades, because a star-seal base or a heavier blend can shift a bag down one row without losing strength.
These ranges assume a household kitchen bin. Where the setting changes, such as a restaurant kitchen, an office, or a municipal collection programme, the same decision applies with a different load profile, and compostable trash bags by scenario walks through each case.
Why wet food needs more than dry waste
Weight is only half the reason wet waste needs a heavier gauge. The other half is what water does to the film while the bag sits in the bin.
A compostable film is designed to interact with water, which is how it breaks down later. That same property means a bag holding wet scraps for two or three days is softer and less resistant to a tear than the same bag holding paper. The load is also concentrated at the bottom rather than spread, since liquid settles.
There is a third factor that rarely gets mentioned. Food waste starts fermenting within a day or two in a warm kitchen, and the gas produced pressurises the bag from inside. A thin film with a weak seal will open at the seam before it ever tears at the panel. This is why a heavier gauge and a good seal belong together, and why upgrading one without the other often disappoints.
Why bag size changes the answer
Two bags at the same gauge do not carry the same load. A 13-gallon bag filled with kitchen waste holds roughly three times what a 4-gallon bag holds, and the film at the base carries proportionally more weight.
The practical rule is to step up one gauge when moving from a small bin liner to a full-size kitchen bag, and to step up again for anything above about 20 gallons. Buyers who standardise on a single gauge across a full range of bag sizes usually end up over-specifying the small sizes and under-specifying the large ones.
The cost of over-specifying
Most buying guides push towards thicker film. In a compostable programme, that advice has a price that does not appear on the quote.
Thicker film costs more per bag, since resin is the dominant cost and the bag uses more of it. It also adds material to the composting stream for no functional gain, which works against the reason the bag was specified in the first place. And as the previous section explained, a heavier gauge can fall outside a certificate scope that was tested at a lighter one.
The useful question is not “what is the thickest bag available” but “what is the lightest bag that survives my waste stream”. A supplier who answers that question with a test rather than a catalogue is doing the more useful job.
Does Thicker Always Mean Stronger?
Quick answer: No. Strength is set by the seal, the resin blend, the puncture resistance, and the thickness together, and thickness is only one of the four. A 30 micron bag with a cold seal fails at the seam long before a 20 micron bag with a correct seal fails anywhere. Thickness buys load capacity and puncture margin, not immunity from a bad weld.
Where a bag actually fails
Watch a full bag being lifted and you will see four failure points, and only one of them is about panel thickness.
The seal line. The weld between two layers is the weakest plane in most bags. If the sealing temperature, pressure, or dwell time is wrong for the film, the seal is under-fused and peels apart under load. A thicker film needs a different heat setting, so increasing gauge without adjusting the seal can make a bag weaker rather than stronger.
The base. In a flat-sealed bag, the bottom corners collect the load. In a star-seal bag, the load is spread across a wider area, which is why a star-seal bag can match a flat-seal bag at a lower gauge.
Puncture points. A bone, a shell, or a broken glass edge concentrates force on a few square millimetres. Thickness genuinely helps here, and it is the one place where the extra micron earns its cost.
The handle or tie. Handles tear away from the body when the weld area is too small for the load, regardless of how thick the panel is.
What thickness cannot fix
Thickness does not compensate for three things, and buyers routinely expect it to.
It does not fix a badly fused seal. It does not fix a brittle formulation, such as a PLA-heavy blend with too little PBAT, which cracks instead of stretching. And it does not fix a bag that is simply the wrong size for the bin, where the film is stretched over the rim and abraded every time the lid closes.
Where thickness does earn its place
Two situations justify stepping up a gauge. The first is puncture risk, where sharp waste is predictable. The second is a long residence time under static load, such as a bag that sits full for several days before collection, since film creeps under sustained weight and a thin bag will slowly elongate at the base.
The practical conclusion is that gauge and seal should be specified together, and that a supplier who will only quote thickness is answering half the question. For the full argument on how seal, resin, and construction interact, see why thicker garbage bags are not always stronger.
How Thickness Affects Compostability and Certification
Quick answer: Compostability is certified for a finished product at a tested construction, not for a resin in the abstract. The main standards are EN 13432 in Europe, ASTM D6400 in the United States, and AS 4736 in Australia for industrial composting, and AS 5810 plus OK Compost Home for home composting. A change in gauge can take a bag outside the tested scope.
What the standards actually require
All three industrial standards test the same four things, and none of them specifies a minimum or maximum thickness as a standalone number.
| Test | Requirement | Standard reference |
| Biodegradation | 90% of organic carbon converted within 6 months under industrial conditions | EN 13432, ASTM D6400 |
| Disintegration | 90% of material passes a 2 mm sieve within 12 weeks | EN 13432, ASTM D6400, AS 4736 |
| Ecotoxicity | Finished compost supports plant growth, tested against a blank | EN 13432 (OECD 208), AS 4736 adds an earthworm test |
| Heavy metals | Below regulated limits for the destination market | All of the above |
The home composting standards run on a slower clock because a garden heap does not reach thermophilic temperature. AS 5810 and OK Compost Home allow around 26 weeks for disintegration and up to 12 months for biodegradation at ambient temperature.
Why gauge changes the test outcome
A thicker film carries more polymer into the same test window. Disintegration is measured against a fixed 12-week limit, so a bag at the top of a certified range has less margin than one at the bottom. This is why a supplier who increases gauge for strength reasons may need to revisit the test evidence rather than assume the certificate still applies.
Formulation matters as much as gauge. A heavier bag with a higher starch or mineral filler content can disintegrate faster than a thinner bag with a high PLA ratio, because the filler breaks the film structure open. Thickness and formulation are a single decision, not two.
What to ask for on the certificate
Ask for four things and check that the numbers line up with what you are buying. The certificate should name the finished product type rather than only the resin. It should state the construction and any gauge or weight range covered. It should name the test standards used. And the test reports behind it should be available, not only the certificate front page.
For the market-by-market breakdown of which certificate applies where, see the compostable bag certification guide.
How to Verify Thickness Before Ordering
Quick answer: Verify three things before you place an order. A multi-point thickness measurement with the method stated, mechanical test data for tensile, tear and seal strength, and a written tolerance band. A single nominal figure on a quotation is not a specification, and two suppliers quoting the same number can be delivering film that differs by fifteen percent.
The five numbers to request
Ask for these in writing, and treat a supplier who cannot provide them as a risk rather than a bargain.
- Nominal gauge and tolerance, stated in microns, with the measurement method named.
- Tensile strength in machine and transverse directions, since film is not equally strong in both.
- Elmendorf tear or dart impact, which predicts puncture behaviour better than tensile strength does.
- Seal strength at the specified sealing temperature, because this is where most bags actually fail.
- Certified gauge range, so the thickness you order sits inside the tested scope.
How to test a sample properly
A sample test that reproduces the real failure is worth more than a datasheet. Fill the bag to the working load you actually expect, not to the breaking point, and hang it for the residence time it will see in service. Then inspect the seal line and the base corners rather than the middle of the panel.
For wet waste, add a second test. Load the bag with wet scraps and leave it for three days before lifting, because film softens with moisture contact and a bag that passes dry will sometimes fail wet. ShinHigh reports the gauge, the seal strength, and the result of both tests with the sample, so a buyer can compare a measured bag against the specification rather than against a description.
What to write into the purchase order
Specify the gauge in microns with the tolerance, the seal strength minimum, the certification scope, and the standard the bag is certified to. Leaving the gauge as a single number invites a supplier to ship the bottom of the tolerance band, which is legal and disappointing.
Conclusion
Thickness is a number you can measure and a decision you cannot make alone. The gauge that works depends on the load, the waste type, the seal, the resin blend, and the certificate scope, and the right answer is the lightest gauge that survives your waste stream inside the certified range rather than the heaviest bag in the catalogue.
ShinHigh Technical Team writes this guide from the production side. ShinHigh Bio, registered as Dongguan Xinhai Environment-Friendly Materials Co., Ltd, manufactures compostable bags and film in Dongguan, China, and holds ASTM D6400, EN 13432 and OK Compost certification for its compostable grades.
If you are specifying compostable trash bags for a kitchen, a restaurant, or a municipal programme, request a quote and a sample pack with the gauge, seal strength, and certification scope stated for your market. Testing a sample against your own waste stream takes less time than correcting a specification after the first container arrives.
FAQ
How thick is a compostable trash bag in microns?
Most household compostable kitchen bags fall between 18 and 30 microns, which is 0.71 to 1.18 mil. Light dry waste can go down to about 15 microns, and heavy or sharp waste usually needs 25 microns or more. The right figure depends on load and seal quality rather than on a single industry standard.
Is 1 mil the same as 25 microns?
Close but not exact. One mil is one thousandth of an inch, which equals 25.4 microns. A bag sold as 1 mil is therefore about 25 microns, and a bag sold as 0.8 mil is about 20 microns. Because suppliers round in different directions, always compare quotes in the same unit.
What thickness compostable bag should I use for kitchen waste?
Start at 20 microns for a standard kitchen bin holding mixed food scraps, and step up to 25 microns if the bag will sit for several days or carry heavy wet loads. For a small under-sink bin with light dry waste, 18 microns is often enough.
Are thicker compostable bags stronger?
Not automatically. Thickness improves puncture resistance and load capacity, but the seal line is where most bags fail, and a thick bag with a cold seal is weaker than a thin bag with a correct one. Resin blend matters too, since a brittle formulation cracks regardless of gauge.
Do compostable bags need to be thicker than plastic bags?
Usually yes, by a margin that depends on the blend and the construction. PLA is stiff with low elongation, and PBAT adds flexibility at lower strength, so a compostable film generally needs a heavier gauge than polyethylene to reach the same load rating. The often-quoted 15 to 25 percent figure is a rule of thumb rather than a standard.
Why do suppliers quote different thickness ranges for the same use?
Because they are answering from different assumptions. Blend ratio, bag construction, the failure they are designing against, and the certificate scope all shift the answer. Two suppliers can both be correct for their own product and still give you ranges that do not overlap, which is why a sample test against your own waste stream settles the question faster than comparing catalogues.
