When the stick sticks: wall adhesion, shrinkage and an elevator that just spins

A balm gripping the tube wall harder than the elevator will not rise. Fill temperature, shrinkage and cohesion, with a warming test and the formula change.

The complaint arrives in two forms. Either the base will not turn at all, or it turns freely and endlessly while the stick sits exactly where it was. Those two symptoms point at opposite ends of the same balance, between how hard the balm grips the barrel wall and how much force the stick can carry without tearing itself apart. Read which side of that balance failed and the fix is obvious. Guess, and you will reformulate a batch whose only problem was a thermometer.

• Pour window: 65-72 C
• Fill 1-2 mm below the rim
• Cure 24-48 h before judging
• Test: 30 s in a closed hand

Adhesion against cohesion: the only question that matters

Winding a stick up applies a shear force along the barrel wall. That force has to break one of two things: the bond between balm and polypropylene, or the balm itself. Whichever is weaker gives way first, and the two failure modes look completely different to the person holding the tube.

If the bond to the wall is weaker, the stick releases as a clean cylinder and rises. That is a working lip balm, and the vocabulary is the same one used for glued joints: adhesive failure at the interface against cohesive failure through the body of the material, as classified in standards such as ASTM D5573.

If the balm is weaker, the elevator pushes and the stick shears internally. A soft, oil-rich formula does this quietly: the disc plows upward through the balm, cutting a plug and leaving a sleeve of material welded to the wall, and nothing appears above the rim. A firm, brittle formula does it noisily, breaking off a chunk that then jams sideways. Both are cohesive failures, and both are cured by making the stick stronger rather than by making the tube slipperier.

Two numbers frame the balance. Polypropylene has a low surface energy, around 29 to 31 mN/m by the wetting tension method of ISO 8296, which is why nothing much sticks to it in ordinary use. Molten balm has a surface tension in the same region, 25 to 33 mN/m, so it wets that surface readily instead of beading off it. The wall is not naturally sticky. It becomes sticky when hot balm is given the time and fluidity to flow into every feature of the moulded surface, and the whole of the rest of this page follows from that.

What a hot fill really does to the barrel

The usual explanation is that filling above 75 C softens the tube wall and welds the balm to it. The direction is right and the mechanism is not, and the difference changes what you do about it.

Polypropylene does not soften at 75 C in any sense a plastics engineer would recognise. Its Vicat softening temperature, measured under ISO 306 or ASTM D1525, runs somewhere around 85 to 100 C for a homopolymer, and its deflection temperature under a 0.45 MPa flexural load, by ASTM D648, is higher still. A 75 C fill leaves the barrel structurally intact.

What a 75 C fill does do is threefold. It gives the melt a low enough viscosity to flow into the fine texture the mould tool left on the bore, which is a mechanical key rather than a chemical bond. It keeps the balm liquid for long enough to complete that flow instead of gelling on contact. And it warms a thin injection-moulded wall enough to let some of the frozen-in moulding stress relax, which is why moulded shrinkage is a specified property with its own test method, ASTM D955, and typically runs 1.0 to 2.5% linear for polypropylene. A wall that relaxes slightly against a stick that is about to contract is a wall the stick will be pressed hard against.

The practical consequence is that lowering the pour temperature attacks all three at once, and nothing else you can do at the bench attacks any of them. It is the same lever that stops balm running past the elevator disc and leaking out of the base, which is why a hot-filled batch often arrives with both faults at the same time.

The cold half: shrinkage away from the elevator plate

The elevator disc is not a flat plate. Almost every design carries ribs, a cross, or a ring of holes on its upper face, and their only purpose is to key the balm to the disc so that pushing the disc pushes the stick. That key is formed by molten balm flowing around the ribs and setting there.

Then the balm contracts. Take the site's working figures: a molten balm near 0.86 g/mL setting to about 0.92 g/mL is a volume contraction of roughly 6.5%, which is about 2.2% linear. On an 11.5 mm bore that is a quarter of a millimetre off the diameter, and along a 55 mm stick it is more than a millimetre of length. If the balm is gripping the wall firmly, that contraction cannot happen freely, so it is taken up as tension inside the stick, and the weakest interface in the system loses. Frequently that interface is the thin balm bridging the elevator ribs, because it is the last material to set and the most constrained.

The result is the spinning tube. The mechanism turns normally, the disc rises normally, and it rises inside a stick that is no longer attached to it, either shearing a channel up the middle or simply travelling up a void that was already there from the pour. A hollow core left by a hot fill makes this far more likely, which is the link between this fault and tunnelling and dips: the same superheat produces the cavity and the wall bond that together guarantee a spinner.

Thermal contraction after setting is a much smaller effect and it is often blamed wrongly. Solid wax blends and polypropylene have linear thermal expansion coefficients of the same order, near 1 x 10^-4 per kelvin, so a tube that gets cold contracts along with the balm inside it. Cooling a stuck tube in the fridge is therefore not a fix. The gap you are hoping for does not open.

Find out which failure you have in one minute

1. Try winding down first. If the base turns down and then up again with normal resistance and the stick moves, there was never a fault: the elevator was simply at the end of its travel.
2. Feel the resistance. Heavy, gritty resistance means the mechanism is loaded and something is holding. Free spinning with no resistance at all means the drive is not reaching the stick.
3. Hold the tube in a closed fist for 30 seconds. Skin runs about 32 to 34 C, so the barrel and the outer few millimetres of the stick come up to roughly 30 C. That is enough to drop the yield strength of a wax network sharply without melting anything.
4. Try again. If it now winds, the mechanism is sound and the diagnosis is wall adhesion. If it still will not move, or still spins, the fault is mechanical or the stick has separated.
5. Sacrifice one tube. Cut it lengthwise with a warm blade. Five seconds of looking answers what an hour of theorising will not: a hollow core, a sleeve of balm left on the wall, a clean gap above the elevator disc.

Rescuing the tubes you already poured

Whether the batch is worth saving depends on which row of that table you landed on. Adhesion is often recoverable in place. Separation from the elevator is not.

For adhesion. Stand the tubes somewhere at about 28 to 30 C for 20 minutes, a warm room or the top of a fridge, then wind each one up about 3 mm and back down 1 mm. That first movement is the expensive one, because it breaks the bond along the whole length of contact. Once broken, it does not reform, and the tube behaves normally for the rest of its life. Do it before the tubes go in a box, not after they reach a customer. Then leave them upright to return to room temperature.

For separation or a hollow core. There is nothing to rescue in place, and the honest move is to decant. Remelting is safe as a process: waxes and refined vegetable oils are not degraded by a second pass through 70 to 80 C, so the reprocessed batch is not a compromised one. The exceptions are a batch that already smells rancid and one carrying heat-sensitive botanicals or actives, where reprocessing changes more than the texture.

1. Wind each stick fully up and cut it off level with the rim. Warm the remainder to about 40 C and tip it out, or push it out from below with the base wound up.
2. Combine the whole run in one vessel. Rescuing tube by tube guarantees an inconsistent batch and makes the result impossible to interpret.
3. Remelt to 70 to 80 C and hold until completely clear. A water bath and a probe thermometer in the melt, not an infrared reading off the surface.
4. Adjust the formula if the diagnosis was cohesive. To take a 100 g batch from 12% to 14% wax by addition, solve (12 + x) over (100 + x) equals 0.14, which gives 2.3 g. The wax ratio calculator handles other starting points, and the sensible bands for a tube formula are set out on lip balm ratios.
5. Add heat-sensitive materials below 50 to 60 C, then repour at 68 to 72 C into fresh tubes with every elevator wound fully down.
6. Cool upright at room temperature, cure 24 to 48 hours, then wind three tubes from the batch. A stick tested at two hours reads softer than the same stick at two days.

Preventing it at the fill bench

Filling to the very brim is a specific cause worth naming. Balm that touches the shoulder or the outside of the rim bonds to a surface the elevator can never push against, so the top of the stick is anchored while the rest of it is trying to rise. It also fouls the cap seat. The tray-and-scrape method and the deliberate top-up pour on filling lip balm tubes both exist to give a level top without a rim smear.

Cooling deserves a word too, because the advice given for grainy butters points the other way. Fast cooling is right for controlling crystal size in a shea-heavy formula. It is not right for a tube, because a stick that contracts quickly against a wall it is bonded to concentrates all that contraction into a short interval, and the interface that fails is not the one you want. Room temperature, upright, undisturbed for the first ten minutes, is the working rule for tubes, and the reasoning behind each window is on pour temperatures.

Formula levers, and what each one costs

Process fixes the majority of these batches. Where a formula is genuinely marginal, four levers are worth having, and each has a price.

The castor lever is worth stating precisely, because the common explanation is wrong. Castor oil does not glue itself to polypropylene: a low surface energy plastic is an unpromising substrate for a polar, hydroxyl-rich oil. What castor does is make the whole balm tacky and viscous, and a tacky stick drags along any wall regardless of what the wall is made of. That tack is also exactly why castor is in almost every lipstick, so cutting it is a real cosmetic trade rather than a free win, and the optical half of that trade is set out on lip colour and gloss physics.

If you are reaching for more wax, measure rather than guess. Penetrometry under a method such as ISO 2137 gives a repeatable number for a stick, and a cheap consistent proxy is described on measuring balm hardness. Deciding by feel is how a batch ends up in the fault opposite to the one you started with, described on balm too hard or too soft, or brittle enough to snap, as on cracked and crumbly balm.

Where the tube is the problem, not you

Some of these faults are bought rather than made. A base collar that disengages, a stripped drive, an elevator disc that will not seat at the bottom, or a bore so oval that the disc binds on two sides are all moulding faults, and no pour temperature fixes them. The test is simple: take three empty tubes from the same bag and wind each one from the bottom to the top and back. If any of them binds, clicks or spins free while empty, the balm was never involved, and the component choice itself is worth revisiting from the packaging guide.

Tube design also sets a floor on how firm your formula has to be. A wax network in a slim tube has to carry its own weight and the push of a small threaded drive, which is a genuinely different demand from a balm in a tin that only has to sit still. That is the physical basis of the different wax bands on tube against tin, and the network behaviour behind it is on oleogels and wax networks.

The decision rule, and the limits of it

Warm the tube in your hand for 30 seconds. If it frees, the mechanism is sound and you have an adhesion problem created at the pour, so lower the fill temperature and stop filling to the brim. If it spins, cut a tube open: a void or a clean gap above the disc means a hot fill and no top-up, and a sleeve of balm on the wall with a plug missing from the middle means the stick is too weak, so add wax. If an empty tube from the same bag misbehaves, the supplier owns the fault.

Two honest limits. First, no published standard covers the winding force of a cosmetic twist-up tube, and no supplier publishes disc interference or bore tolerance, so the balance between adhesion and cohesion cannot be calculated in advance for your particular hardware. It has to be measured, six tubes at a time. Second, the trade is real in both directions: every point of wax that stops a stick shearing also makes it drag on the lip, and the pages on drag and poor glide and this one describe opposite ends of one dial. A stick that always winds smoothly and never applies well is not a solved problem.

Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.