Milk pouch film explained: why most milk pouches are multilayer

In India most of us buy milk in a pouch every morning, cut the corner with scissors and pour it into a pan without a second look at the film in our hand.

That film has a harder job than it looks.

Most milk pouch film is two or three layers of polyethylene, made together on a blown film line. Each layer gets its own job. The inner one, the layer that melts in the sealing jaws, matters most, because that is where a pouch either holds or leaks. Splitting the work this way is how dairies get strong seals and few pinholes from a thin film.

I run Jagannath Polymers in Jaipur. We have been making packaging since 1997, and today we make multilayer blown film on our own line. This guide is what I would tell a dairy supervisor who has to specify milk film for the first time.

What is milk pouch film made of?

Polyethylene. Let us start with the standard, because it answers most of the basic questions. The Indian standard for milk pouches, IS 11805:2007 (BIS, second revision, October 2007), says the pouches shall be made from virgin LDPE, LLDPE or a blend of the two. The plastic must meet the food-grade standard IS 10146, and any pigment must come from the list in IS 9833.

Let us take the two grades one by one, because they behave differently:

1. LDPE (low density polyethylene) is soft and easy to run, but on its own it makes a weaker seal and tears more easily.
2. LLDPE (linear low density polyethylene) is tougher. It stretches more before it breaks, and it seals stronger.

Indian dairies moved from LDPE to LLDPE years ago, and fewer leaks was the first reason given. A chapter by K R Kumar of CFTRI, Mysore, in ICPE's book Plastics in Food Packaging (undated), reports average leakage losses of 1 to 5% with LDPE film against 0.6% with LLDPE film. The same chapter names a co-extruded 50:50 blend of LDPE and octene LLDPE as the common milk film of its time.

Why is milk film made in layers?

On a blown film line we can push two, three or more melts through one round die at the same time, and they come out as one film with separate layers. We call this co-extrusion. Each layer can then be given its own recipe:

1. The outer layer is treated so ink sticks to it. It also carries the slip that lets film run over the forming collar. IS 11805 sets the kinetic coefficient of friction at 0.25 or less.
2. The middle layer is mostly there for strength and body.
3. The inner layer is the sealant. It has to melt quickly in the jaws and hold the weight of the milk while the seal is still warm. We film makers call that hot tack. Weak hot tack can show up as a bottom seal that pulls open the moment milk lands on it.

Layers also help with pinholes. A tiny hole or a gel in one layer rarely lines up with a hole in the next layer. ICPE's own note on packaging of milk and dairy products (undated) gives exactly this as the reason dairies use co-extruded LDPE-LLDPE film.

A fair question at this point: is a three-layer milk pouch still one material?

Yes. Every layer is polyethylene, only in different grades, which is why IS 11805 asks for recycling symbol No. 4 on the pouch.

How thick should milk pouch film be?

IS 11805 does not fix one number. It says you, the purchaser, should specify the thickness, judged by the leak and drop tests on filled pouches. Then it gives a floor:

1. Not less than 50 micron for 1 litre pouches.
2. Not less than 40 micron for half litre pouches.
3. Tolerance of plus or minus 7.5% on whatever thickness you specify.

I read that floor as a safety minimum, not as a target for every application.

Here is a rule of our trade that every dairy should know. You buy film by the kilo, but you use it by the pouch. A thinner film gives more pouches from each kilo. The same CFTRI chapter did the sum for us: cutting the film by just one micron gives 9 more half-litre pouches, or 6 more one-litre pouches, from every kilo.

I am in favour of going thinner, with better resins, when the tests allow it. I am not in favour of going thinner because a purchase sheet says so. Decide the thickness with a drop test on your own line, in your own crates. We would give the same advice to any dairy, whoever supplies the film, because a pouch that bursts in the crate costs far more than the few grams of plastic it saved.

I will also admit something about my own industry.

No blown film line in the world makes a perfectly even film, and ours is no exception. The bubble always has slightly thin and slightly thick zones, which is why IS 11805 allows 7.5% either way. So check the thinnest point across the roll width, not the average.

White film or black-white film?

Light spoils milk.

Riboflavin (vitamin B2) in milk absorbs light and sets off oxidation, and the result is an off-flavour and some loss of vitamins.

A study from Norway in the Journal of Dairy Science (Intawiwat and others, 2013) put it plainly: to keep milk quality, blocking all visible light would be best. Plain white film does not do that. The CFTRI chapter reports that a black pigmented pouch passing less than 1% of visible light worked very well, while polyethylene jugs with 2% titanium dioxide (the white pigment) did not protect the milk well.

That is the logic of black-white film. The inner layer carries black pigment and stops the light, while the outer layer is white, so the pouch still looks clean and takes print. It is the same reason the old black umbrella gives darker shade than a thin white cloth.

I would not push black-white film on every dairy. It is worth testing when:

1. Your pouches sit in lit shop fridges for hours.
2. You are selling milk with a longer date on the pack.
3. You have had complaints about an off taste in pouches that were kept cold.

It has limits. It usually costs more, the customer cannot see the milk, and it does nothing about warm storage. FSSAI's guidance document for milk and milk products (first edition, February 2018) keeps pasteurised milk below 5°C from the plant to the retail shelf.

No film can fix a broken cold chain.

If you want to understand what film can and cannot block, read our guide to OTR and WVTR in plain words.

What should you write on your film order?

A vague order such as "milk film, 55 micron, white" invites trouble. If a dairy asked us for film tomorrow, these are the details we would need first, and they are the lines I would put on the purchase order:

1. Material: virgin LDPE and LLDPE, food grade to IS 10146, pigments to IS 9833.
2. Structure: number of layers and the colour of each, for example white outside and black inside.
3. Thickness and the tolerance, plus the pouch size it is for.
4. Width with tolerance, core size, roll weight, and no telescoping of the roll. IS 11805 covers width, winding and the core.
5. Slip: kinetic coefficient of friction of 0.25 or less.
6. Test values for every lot: tensile strength, elongation and dart impact, as listed in IS 11805.
7. Printing ink to IS 15495. The FSSAI Packaging Regulations, 2018 (compendium version IV, 9 September 2022) require this ink standard and say the printed surface must not touch the food.
8. A certificate of conformity from a NABL-accredited lab for the food-contact layer, as regulation 3(14) of the same rules requires.

IS 11805 also has a simple ink test you can copy. Soak a printed piece of film in milk for 12 hours at about 8°C, then wipe it dry and rub it gently with tissue paper, and the print should still be readable.

Checks your team can do when film arrives

You do not need a lab for the first round of checks. These are the five we would start with:

1. Hold a sheet against a tube light and look for pinholes, gels (small hard specks), streaks and bands of uneven thickness, which IS 11805 lists as defects.
2. Measure thickness with a micrometer at five or six points across the width, and write down the lowest reading, not the average.
3. Smell the inside of the roll. The standard asks for film free of any foreign odour.
4. Look at the roll edges, which should be trimmed clean and wound evenly with no layers sliding out.
5. Store rolls off the floor in a clean, dust-free room. The FSSAI guidance says packaging material should never sit directly on the floor.

Then run the leak and drop tests from IS 11805 on the first filled pouches. I have explained both, step by step, in our guide on why milk pouches leak.

If you are reviewing your milk film, send us your pouch size, your machine type and how long the milk sits on the shelf. We will suggest a structure you can trial on your own line.