How thick should a dog poop bag be? A guide to microns, film and the number nobody prints

Dog poop bag thickness is the only specification that decides whether a waste bag does its job, and it is the specification the category has quietly agreed to stop printing. We know that because we measured it. We bought nine boxes, took three bags out of each, put a digital micrometer on the mid panel away from the seam, and found that seven of the nine printed no film gauge anywhere: not on the box, not in the listing, not on the brand's own website. Two of those seven used the phrase "extra thick" on the front of the box. One used "heavy duty" twice.

This article is the plain-language version of what that number means, so you can judge a bag without owning a micrometer.

What a micron actually is

A micron is one thousandth of a millimetre. Film gauge is the thickness of the plastic wall of the bag, and in the rest of the world it is quoted in microns. In the United States it is sometimes quoted in mils instead, where a mil is one thousandth of an inch. The conversion is the only arithmetic you need:

• 1 mil equals 25.4 micron
• 15 micron equals roughly 0.59 mil
• 20 micron equals roughly 0.79 mil

Those numbers sound small because they are small. A supermarket carrier bag sits around 9 to 12 micron. The thinnest bag in our nine was 9 micron. The thickest was 19. Our own bag is 15, which we print on the front of the box next to the count, because if we are going to argue that the number matters then we had better publish ours.

Why thickness is the whole argument

A waste bag has one job and one failure mode. It either holds, or it does not and you find out at the worst possible moment. Everything else a box can claim is secondary to that, and most of it is decoration.

Thickness drives three things that you notice in the hand:

Puncture resistance. The practical failure is rarely a tear along a straight line. It is a small sharp point, a stick or a piece of gravel picked up with the waste, pressed through the film by your fingers. Thicker film tolerates more of that.

Stretch before failure. Thin film goes to its limit quickly and then goes all at once. Thicker film gives you warning, which in practice means you notice the strain and adjust your grip before anything happens.

Opacity. This one is aesthetic and nobody admits to caring about it. Thinner film is more translucent. At 9 micron you can see the contents clearly. At 15 you mostly cannot.

Why nobody prints the gauge

Because the words are cheaper than the film. "Extra thick" costs nothing to add to artwork. Two extra microns of high density polyethylene across a production run of a million bags costs real money. In a category where almost nobody publishes a figure, there is no comparison the shopper can make, so the words win and the film gets thinner.

That is not a conspiracy. It is just what happens to a specification when no one is required to state it. There is no labelling rule in the United States that compels a waste bag seller to publish film gauge, in the way that a food label has to carry a nutrition panel.

The one place the Federal Trade Commission has gone after this category is environmental claims rather than thickness. In February 2015 the FTC sent warning letters to dog waste bag marketers telling them their biodegradable and compostable claims likely violated the FTC Act. The letter is short and worth reading in the original. It says that to claim a product is biodegradable without qualification, a seller needs "competent and reliable scientific evidence that it will degrade in most landfills within the claimed time period," or within one year if no period is stated, and it notes the obvious problem that material sent to landfill or incineration does not biodegrade at all. You can read the letter on the FTC's own site, and the underlying rule is at 16 CFR 260.8.

We bring that up here for one reason. If the regulator has had to write to this category about the claims on the front of the box, then the claims on the front of the box are not a reliable way to choose a bag. The number on the back is.

How to judge a bag without a micrometer

You will usually be standing in a shop or looking at a listing, with no instrument and no published figure. Three tests get you most of the way.

Hold one bag up to a light. Not the roll, a single bag. If you can read print through two walls of the film easily, you are at the thin end of the category. This is crude and it works.

Listen to it. Crinkle a bag next to your ear. High density polyethylene is stiffer per micron and sounds sharper and louder. Low density polyethylene is softer, quieter and stretchier. This tells you the material rather than the thickness, but material and thickness interact: a 15 micron HDPE bag feels more substantial than a 15 micron LDPE bag, while the LDPE one will stretch further before it gives.

Weigh the roll in your hand against the count. A 270 bag pack and a 300 bag pack of the same dimensions should not feel the same. If a pack with more bags in it feels lighter, the film is thinner. You are measuring mass, which is thickness multiplied by area, and area is printed on the box.

The dimension nobody checks

Thickness is not the only number. Bag dimensions decide whether the thickness ever gets tested. A bag that is too small forces you to stretch the film to its limit and to get your hand closer to the contents than you want. A bag that is comfortably oversized never sees the load that would break it.

Ours are 13 by 9 inches, which is a deliberate compromise rather than a boast. For a dog under about 60 pounds that is generous, and the film is barely working. For a very large breed, or for two dogs on one walk, it is adequate rather than roomy, and you will be tying the handles closer to the top.

So how thick is thick enough?

Here is our honest answer, including the part that does not help us.

Up to around 12 micron is carrier bag territory. It works for a small dog on a dry pavement and it is why the cheapest bags on the shelf are cheap. It is also where almost all the failures live.

15 micron is where we sit. It covers the great majority of dogs and conditions. It is also, and we want to be straightforward about this, a choice about bulk as well as strength. Thicker film makes a fatter roll, and you carry that difference on every walk, in a pocket or clipped to a lead.

19 to 20 micron is genuinely more bag than most dogs require. If you have a very large breed, or you walk somewhere with a lot of sharp debris, or you simply want more margin, buy a 20 micron bag from someone else. We do not make one and we are not going to talk you out of wanting one.

What we will not do is tell you 15 micron is the right answer for everybody, because it is not. It is the right answer for most people, which is a different and smaller claim.

What we have not tested

A gauge figure and a load test are two different claims and we are not going to let one stand in for the other. We have measured film thickness on nine brands. We have not drop tested any of them, we have not puncture tested any of them, and until we do we are not going to imply that 15 micron outperforms 12 micron by any particular margin. It should. We have not shown it.

That test is next, with a published method, and our own bag goes through it on the same day and the same rig as everyone else's. When the numbers exist, they get published here whether they flatter us or not.

The arithmetic, since it is the other half of the decision

Thickness is one axis. Cost per bag is the other, and it is the one you can work out yourself in ten seconds. Our 270 pack is $14, which is about 5.2 cents a bag. The 810 pack is $34, which is about 4.2 cents a bag. A roughly 20 percent saving for roughly three times the storage commitment.

Whether that is a good trade depends entirely on where you live. In a house with a utility cupboard, buy the big one. In a one bedroom apartment, three boxes of bags in a closet is a genuine cost that no spreadsheet captures, and the small pack is the better buy even though it is worse value per bag.

The short version

Thickness is measured in microns, 15 is a sensible middle, and the number matters less than the fact that it is printed at all. A brand that publishes its film gauge has given you something you can check. A brand that writes "extra thick" instead has given you an adjective. If the box you are holding does not state a figure, that is itself the most useful piece of information on the packaging.

Our bags are 13 by 9 inches, 15 micron, unscented, and 65 percent recycled HDPE. Those four numbers are on the front of the box. If a competitor prints theirs and beats us, we would rather you had the comparison.