Glassine, SCK, or CCK: Choosing a Release Liner Base by Cost, Release, and Recyclability

Choosing between glassine, supercalendered kraft (SCK) and clay-coated kraft (CCK) is a decision about where the money goes: into the base, into the silicone, or into scrap. Glassine holds silicone best and costs most per tonne. SCK sits in the middle. CCK closes the surface with a mineral layer instead of pressure, and behaves differently again once the liner reaches end of life.

Nobody sells you all three honestly, because almost nobody makes all three. The comparison usually arrives as a datasheet from whichever mill your indenter represents. This piece scores the three the way a coating technologist has to weigh them: release consistency, silicone consumption, delivered cost, runnability, and what happens to the liner after your customer peels it.

What actually separates glassine, SCK and CCK?

All three start as chemical kraft pulp refined into a dense, well-formed sheet. What separates them is how the surface gets closed. Glassine and SCK close it mechanically under a supercalender. CCK closes it with a clay coating. That one difference drives release behaviour, cost and end of life for the whole liner.

Glassine is a highly refined, heavily supercalendered paper. Long refining develops fibrillation, the sheet is hydrated and dense, and the supercalender stack works it into a translucent, near-closed web. Its defining property is low air permeability, which is why it became the reference release base worldwide.

Supercalendered kraft (SCK) uses less aggressive refining and the same finishing route. It is more opaque, more porous than glassine, and cheaper. The labelling convention catches buyers out: North American converters generally say SCK where European converters say glassine, and a European glassine is often an SCK carrying a polyvinyl-alcohol topcoat to close the surface further. When you compare quotes across regions, compare the air permeability figure rather than the trade name.

Clay-coated kraft (CCK) takes a kraft base and applies a pigment coating, usually kaolin clay with a binder. The coating fills surface voids instead of crushing them shut, so a CCK can reach a closed surface at a lower base density than glassine needs.

So the trade sits between two ways of getting to the same place. A supercalendered sheet is dense the whole way through. A coated sheet is a lighter body carrying a closed skin. Density costs you fibre. A skin costs you a coating pass, and it turns into a repulpability problem later.

Air permeability is the working proxy across all three. Uncoated release base papers in the patent literature are characterised at Gurley values from roughly 300 seconds up to 1,000 seconds and beyond depending on grade, and the higher the number, the tighter the sheet. Gurley air resistance is measured to TAPPI T460 and ISO 5636-5, which time a fixed volume of air through a fixed area at fixed pressure. Bendtsen, the alternative used across much of Europe, runs to ISO 5636-3 and reports the opposite way round, as a flow rate in millilitres per minute, so a high Bendtsen number means an open sheet where a high Gurley number means a closed one. Two mills quoting “low porosity” on different instruments are not quoting the same thing, and converting between the two scales is approximate at best. Ask for the method, the instrument and the sample count alongside every figure.

How does each base change your silicone consumption?

Silicone consumption is set mostly by the base, not by the silicone. An open sheet draws coating into the fibre network, so you lift coat weight to keep a continuous film on the surface and hit target release. On a full-surface cure, typical silicone coat weights sit in the 1-2 g/m² range. Those are small numbers until you notice that a 20% overshoot on a high-volume grade becomes a real annual figure.

The mechanism is not complicated. Cure chemistry only works on silicone that stays where you put it. Anything that wicks below the surface is neither forming the release film nor coming back. That is what silicone holdout names, and holdout improves with both low porosity and low density in the base. Those two do not always move together, which is why a heavy sheet is not automatically a good one.

Ranked on holdout at equal coat weight, the order is consistent: glassine first, CCK close behind where the coating is well formed, SCK last. Ranked on delivered cost per square metre, the order frequently reverses, because glassine’s holdout is bought with fibre and calendering energy that show up in the tonne price.

There is an honest third route that suppliers rarely lead with. Reduced-penetration silicones exist to compensate for a more open base: heavier, more viscous formulations that resist wicking. They cost more per kilogram than a standard emulsion, and they let a converter run a cheaper base without the holdout penalty. Whether that trade wins depends on your silicone contract, not on the paper. Ask both suppliers before you assume the base is the variable worth optimising.

Where this stops holding: holdout is a surface property, and surface properties do not survive bad handling. A base with excellent laboratory holdout that has picked up moisture in transit, or stood on end in a humid shed through a monsoon, will coat unevenly whatever its datasheet says. Reel condition on arrival routinely matters more than the last hundred Gurley seconds of specification.

Decision matrix: how the three bases score for a coater

Scored out of 5 on the five criteria a coating technologist weighs in practice. Higher is better in every column, including cost, where 5 means cheapest delivered.

Read the totals with some care, because they are not a recommendation. The weighting that matters is yours. A label converter running premium graphic stock will weight release consistency at three times cost and land on glassine. A tape or hygiene producer running high volume on tolerant chemistry will weight cost hardest, land on SCK, and spend the saving on reduced-penetration silicone. CCK wins where a lighter body has to carry a closed surface, but only if the downstream chain can handle a mineral-coated liner.

Put plainly: glassine buys predictability, SCK buys margin, and CCK buys a lighter closed surface with an end-of-life cost attached to it.

Which release liner base is cheapest, per tonne or per square metre?

Per tonne, SCK is cheapest and glassine dearest. Per square metre at equal performance, the ranking depends on grammage and on how much silicone each base drinks. Buying release base on tonne price alone is the most common costing error in liner converting, because the liner is sold to your customer by area, not by weight.

Work it through with real numbers. Commercial release bases span a wide substance range: Ahlstrom’s Silco MG coating base is offered from 14 to 98 gsm and the MF grade from 41 to 163 gsm, while delfort’s tersil ultralight release base runs at 35 gsm. General-purpose glassine release base sits around 50-80 g/m². One tonne of 70 g/m² base yields roughly 14,300 square metres; the same tonne at 50 g/m² yields about 20,000, so the lighter grade carries close to 40% more area before anyone has argued about the rate per kilogram. That is the whole commercial logic of lightweighting, and it is also why a mill quoting a lower price per tonne on a heavier sheet can still turn out to be the expensive option once it reaches your costing sheet and your slitter.

Then subtract what the base costs you downstream. A cheaper, more open base that needs 20% more silicone to reach target release has spent the saving before the reel leaves your plant, because silicone is priced per kilogram at a multiple of paper. The costing that survives an audit reads: base cost per m², plus silicone cost per m² at the coat weight that base actually requires, plus waste at the coating and slitting stages. A base paper procurement checklist is where you hold suppliers to those three lines instead of to a headline rate.

Where it stops holding: below roughly 40 gsm the calculation stops being arithmetic and becomes a machine question. Web breaks, tension control and moisture profile start to dominate, and one break on a coating line costs more in downtime than the grammage saved across the whole reel. Lightweighting pays up to the point where your line stays stable, and no further.

Can a silicone-coated release liner be recycled in India?

Not through the ordinary waste-paper stream. A cured silicone layer interferes with standard repulping, and Indian mills buying recovered paper price liner waste accordingly, where they accept it at all. Dedicated liner recovery exists globally through industry programmes such as CELAB, but Indian collection infrastructure for it is thin, and pretending otherwise does your customer no favours.

Between the three bases, end of life separates on what else is in the sheet. Glassine and SCK are fibre plus silicone: a mono-material paper problem, and mills that have invested in liner repulping can process them. CCK carries a mineral coating as well, which raises the ash content of the recovered stock and gives a repulper a second reason to reject the bale.

This is a specification question rather than a marketing one. If your customer carries an EPR obligation or a recycled-content commitment, the liner is part of what they will be asked to account for. Compostability and recyclability are also not interchangeable claims. A base that composts is not automatically accepted at a paper mill, and a liner that repulps is not automatically compostable. Get the claim your customer actually needs in writing before you qualify a base, and keep the receiving mill’s acceptance criteria on file.

How do you test release before you commit to a base?

Test release on your own coating chemistry and your own laminate, at the peel rate your customer uses, before qualifying anything. Datasheet release values are generated on the mill’s silicone and the mill’s face stock, and they transfer poorly. The methods are standardised and cheap to run, which removes most of the excuse for skipping them.

The working set:

1. Release force, to FINAT Test Method No. 10 for low-speed release and FTM 3 for the label industry’s peel geometry. ASTM D6862 covers 90-degree peel where you need a general adhesion-standard reference.
2. Subsequent adhesion, which shows whether silicone has transferred to the adhesive. Rising release force with falling subsequent adhesion is the classic anchorage failure signature.
3. Air permeability, to TAPPI T460 or ISO 5636-5 for Gurley and ISO 5636-3 for Bendtsen. Fix one instrument across all suppliers and hold them to it.
4. Grammage and thickness, to TAPPI T410 and T411, run reel to reel rather than once at qualification.
5. Strength properties, meaning burst and tear, where the lighter grades declare themselves. The burst factor and tear index testing guide covers the methods and what the numbers mean on a converting line.

Run the whole set on three reels from different production dates, not on one hand sheet. Batch-to-batch variation is what actually costs a coater money, and a single sample cannot show it. The same principle governs any release liner base specification exercise, not only a supplier switch.

Where it stops holding: these tests characterise the base and the coating, and they say nothing about shelf life. Silicone systems age, and release force typically drifts upward over months. If your customer stores converted stock for a quarter before use, build an accelerated ageing step into qualification or you will end up diagnosing a field complaint you could have caught in the lab.

What does a food-contact application add to the specification?

Food contact adds compositional and migration requirements on top of the release specification, and they apply to the base as much as to the coating. A liner that never touches food may be out of scope. A base going into a wrap, sachet or dry-food liner is squarely in scope, and the compliance file belongs with the base supplier.

In India the operative reference points are the FSSAI packaging regulations and the relevant BIS specifications. The FSSAI Compendium’s packaging provisions set characteristics for food-grade paper including burst factor of not less than 20, tear factor of not less than 30 in any direction, oil transudation of not less than 1,200 seconds, and grammage of not less than 35 g/m². For printed constructions, IS 15495:2020 is the code of practice for printing inks used on food packaging, and IS 1397:2020 covers kraft paper for packing and wrapping. Check the current edition against the Bureau of Indian Standards catalogue before you write any of these into a purchase specification, because editions get revised and a stale clause in a contract is worse than no clause.

Where it stops holding: a compliant base does not make a compliant pack. Migration behaviour depends on the whole structure, the food simulant, the contact time and the temperature. Your customer’s compliance team tests the finished construction, and that test can fail on an adhesive or an ink while every input carries a certificate. The same logic runs through dry food liner requirements, where the substrate is necessary and nowhere near sufficient.

Where a paper coating base fits

Everything above is a category comparison and it holds regardless of who supplies you. It is also the context in which Pakka is developing flexC base, a coating base paper made on PM4 in a 40-60 GSM band, bleached and unbleached, intended as a substrate for barrier chemistries including silicone, biopolymer and plastic, with target applications named as confectionery wraps, snack pouches, sachets, medical packaging, seed packs, release liners, dry food liners and tea pouches, all as disclosed in Pakka Limited’s Investor Presentation Q1 FY2026-27, filed 18 August 2026 (BSE 516030 / NSE PAKKA).

The limitations come first, because they decide whether any of this is relevant to you. flexC base is a development programme rather than a catalogue item, and no performance data is published for it. No porosity figure, no holdout figure, no release value. Porosity control on a lighter sheet is a hard problem and not one to claim as solved. If you need a qualified base against a fixed specification this quarter, buy a proven grade from a proven mill.

Two names also get conflated often enough to be worth separating. flexC base is the uncoated coating base paper described here. flexC is the finished compostable flexible-packaging laminate Pakka already sells to brand owners, with its own published specifications. Different product, different buyer, different datasheet.

What is worth a conversation now is the specification itself. If you run a coating or laminating line and have a view on what a base in this band would have to deliver before you would put it on your machine, that input is more useful before a grade is fixed than after it. Send it through the Pakka contact page marked as a flexC base trial enquiry and it reaches the material science team rather than a sales queue. Technical documents for the products already in the range sit in the resources library.

Last reviewed: September 2026

Frequently asked questions

Is glassine the same as SCK paper?

Not quite, and the answer depends on which market you are buying in. Both are supercalendered kraft-based release bases. Glassine is more heavily refined and denser, giving lower air permeability and better holdout, while European practice often uses “glassine” for an SCK carrying a polyvinyl-alcohol topcoat. Compare measured air permeability rather than the label.

Which release liner base uses the least silicone?

Glassine, at equal coat weight, because its closed supercalendered surface keeps silicone from wicking into the fibre. CCK is close behind where the clay coating is well formed. SCK is the most open of the three and usually needs either more coat weight or a reduced-penetration silicone to reach the same release.

What grammage does release liner base paper normally run at?

General-purpose release base commonly sits around 50-80 g/m², and commercial grades span far wider: Ahlstrom’s Silco MG base is offered from 14 to 98 gsm and delfort’s tersil ultralight runs at 35 gsm. Lighter grades give more area per tonne but demand tighter web tension and moisture control.

Can release liners be recycled in India?

Not in the standard recovered-paper stream, because cured silicone disrupts repulping and most Indian mills discount or refuse liner waste. Dedicated liner recovery schemes exist internationally, but Indian collection infrastructure is limited. Fibre-only bases such as glassine and SCK are easier to place than mineral-coated CCK.

How do I test a new release liner base before switching supplier?

Run FINAT FTM 10 release force and subsequent adhesion on your own silicone and face stock, plus air permeability to TAPPI T460 or ISO 5636-5, grammage to TAPPI T410 and thickness to TAPPI T411. Use three reels from different production dates so batch variation shows up, and add an accelerated ageing step if the stock is stored.

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