Key takeaways
- Piston fillers suit viscous products; peristaltic pumps suit low viscosity.
- Foaming during fill causes weight variation and bubbles in the pack.
- Fill temperature must be inside the line's tolerance window.
A fill line is a machine with a viscosity window, a temperature window and a tolerance for foam. A formula developed on a bench can be perfectly good and still fail in production because it falls outside one of those windows. The scale-up problem is usually a fill problem rather than a chemistry problem.
1. Filler types
A piston filler draws a fixed volume and is standard for creams and gels. A peristaltic pump suits low-viscosity liquids and is gentler on shear-sensitive formulas. A net-weight filler weighs as it fills and handles variable density. The filler type must match the formula’s rheology.
2. The viscosity window
Most piston fillers handle 5,000 to 100,000 mPa·s comfortably. Below 5,000 the product leaks past the piston; above 100,000 it will not flow into the nozzle. A formula outside the window needs a different filler, not a different formula, and the line’s capability should be known before the formula is fixed.
3. Foaming
Surfactant-containing formulas foam during filling, and foam causes weight variation and visible bubbles in the pack. A slow fill, a bottom-up nozzle and a deaerated bulk tank reduce it. A toner that foams on the line will show bubbles in every bottle.
4. Temperature
A hot-poured product must be filled within a narrow temperature band. A product that cools in the hopper thickens and the fill weight drifts. Heated hoppers and jacketed lines keep the temperature stable, and the tolerance should be in the batch record.
5. Shear sensitivity
Some formulas — gels with a fragile structure, emulsions with a soft interface — break down under the shear of a pump. The viscosity drops and the texture changes. A shear-sensitive formula needs a low-shear pump and a short transfer distance.
6. Accuracy
Fill accuracy is typically ±1 to 2 percent for a piston filler on a viscous product, and ±3 to 5 percent on a low-viscosity one. The declared net weight must account for the tolerance, because a legal-metrology check on the finished pack is unforgiving.
7. Changeover
Changeover between shades or fragrances requires a flush and a purge. A line that does not flush thoroughly contaminates the next batch, which shows up as a shade shift or an off-note. Changeover time is a real cost and should be in the quotation.
8. The nozzle
The nozzle diameter and the fill height determine whether the product fills to the right level in the pack. A wide nozzle on a narrow bottle leaves product on the rim, which contaminates the seal. Nozzle selection is part of the line setup, not an afterthought.
9. Validation
A fill validation run covers three batches and checks weight, seal integrity, label position and appearance. It is the moment when lab formulas become products. A brand that skips validation discovers the problems in the first commercial order.
10. Communication
The filler needs the viscosity curve, the fill temperature, the foam tendency and the shear sensitivity. A brief that says “a cream” leaves the line to guess, and the guess is usually wrong. The technical data sheet is what makes a quotation accurate.
11. Where it fits
Fill compatibility runs across the hand cream range; the viscosity side continues in the viscosity entry.
Reference: Fill line capability data and scale-up records, 2025
