Overview
A controlled comparison between a representative bar soap and a representative liquid soap, assessing lather volume, residue, cleansing efficiency, foam stability, and subjective skin feel.
Materials
- Bar Soap (Sample A)
- Liquid Soap (Sample B)
- Graduated cylinder (50 mL)
- Analytical balance (±0.01 g)
- Stopwatch
- Thermometer or water bath
- Standardized test substrate
- Towels and drying rack
Controlled Variables (Numeric)
- Water Temperature: 28 °C (±1 °C)
- Contact Time: 20 seconds
- Application Pressure: 2.0 kg-force
- Sample Mass/Volume: Bar: 1.0 g / Liquid: 1.0 mL
- Rinse Volume: 500 mL
- Drying Time: 10 minutes
- Replicates: n = 3
Method
- Prepare Samples: Condition samples at test temperature for 30 minutes.
- Weigh/Dispense: 1.0 g bar shavings or 1.0 mL liquid soap per replicate.
- Apply and Rub: Apply using standardized motions and pressure for 20 seconds.
- Rinse: 500 mL at 28 °C, allow to drain and dry for 10 minutes.
- Measure: Record lather, residue, cleansing, foam stability, and subjective feel.
Measurement Criteria
- Lather Volume: mL foam collected in graduated cylinder
- Residue: mass difference before/after drying
- Cleansing Efficiency: % removal of standardized soil/sebum
- Foam Stability: time to collapse to 50% height
- pH (optional): 1% solution
- Skin Feel: subjective 1–5 rating
Scoring System
Normalize each metric to a 0–25 score, total = 100.
- Lather Score = (Sample / Best) × 25
- Residue Score = (1 − Sample/Worst) × 25
- Cleansing Score = (%Removal/100) × 25
- Skin Feel Score = (Rating/5) × 25
Data Table (Replicates)
| Parameter | Bar R1 | Bar R2 | Bar R3 | Bar Avg | Liquid R1 | Liquid R2 | Liquid R3 | Liquid Avg |
|---|---|---|---|---|---|---|---|---|
| Lather Volume (mL) | ||||||||
| Residue (g) | ||||||||
| Cleansing Efficiency (%) | ||||||||
| Foam Stability (s) | ||||||||
| pH (1% solution) | ||||||||
| Skin Feel (1–5) | ||||||||
| Total Score | ||||||||
Download Workbook: Bar vs Liquid Soap Test
This workbook contains the complete set of reproducible data templates for Protocol 1, including the Materials Log, Replicate Measurement Sheet, Scoring Sheet, and Interpretation Guidelines.
⬇ Materials & Variables (CSV)
⬇ Replicates Data Table (CSV)
⬇ Scoring Sheet (CSV)
⬇ Interpretation Notes (CSV)
Download Full Workbook (ZIP)
You can download all CSV templates as a single ZIP archive:
📦 Download Complete Workbook (ZIP)Interpretation Guide
- Higher score = better overall performance.
- Low residue → better rinseability but may reduce moisturization.
- Lather volume must be considered with foam stability.
- If results are similar, increase replicates to n=5 for tighter confidence.
Notes & Limitations
- Use the same operator when mechanical control is not available.
- Document any deviations from constants (like water temperature).
- This protocol is for consumer-facing comparison, not clinical validation.