Cosmetic Sachet Stability Tests: Build a Useful Control Matrix

A buyer considering a new sachet may ask whether the proposed structure behaves differently from the current pack. Another project may be investigating a formula change. These questions need different comparisons. Write down the decision the study should support, the factors intentionally changed and the factors the laboratory intends to hold comparable.

ISO/TR 18811:2018 explains that cosmetic stability testing has no universal conditions or criteria for every product; manufacturers must define and justify their approach. The public summary is not a complete test protocol. Ask the responsible specialists to set the study design and acceptance criteria for the actual formula and package.

The March 2004 Cosmetics Europe/CTFA stability guidance discusses representative marketed packaging and deliberate selection of suitable controls. A reference container is useful only if its own behavior is understood for the investigation. Glass, for example, should not be assumed to be universally inert.

The following original worksheet organizes a discussion with the laboratory. It does not prescribe a testing service, sample count, exposure schedule or passing result. Use only comparison groups that the study owner can justify.

Assign a sample identifier before recording observations. If candidate sachets use a different formula batch, fill volume or closure process from the reference group, make that difference explicit. Otherwise, a later reviewer may attribute a change to the package when the comparison also changed something else.

Record which observations belong to the product, the package or the combined system. For example, a change in appearance and a seal defect are different observations even if they occur in the same sample. Keep photographs and measured results linked to the laboratory’s methods and sample IDs, rather than merging them into one unexplained pass/fail label.

In a hypothetical comparison, a change appears in the candidate sachet but not in the current pack. That result can justify further investigation of the changed configuration. It does not establish a root cause without checking the study design, sample preparation, measurement and other differences. If every comparison changes, that also needs interpretation rather than an automatic conclusion that packaging is irrelevant.

Have the study owner document what is supported, what remains unresolved and which evidence is needed before production approval. Do not convert an accelerated-study duration into a promised shelf life using a generic multiplier. Keep the agreed confirmation work and real-time observations in the project record.

For a broader purchasing brief, see the cosmetic packaging compatibility guide. Layer-interface reports belong in a separate laminate-bond review; they do not replace the product-and-package study.

When discussing custom sachets and stick packs, send the formula category, proposed sachet size and structure, intended use and laboratory-approved sample requirements. Identify whether samples are for appearance, filling development or the defined study. P&M’s packaging discussion is not a claim that your formula has already passed testing or that laboratory services are included.