How to Make Dual Lye Soap
A Complete Guide to Cream Bars and Shaving Soaps
What is Dual Lye Soap?
Dual lye soap combines sodium hydroxide (NaOH) and potassium hydroxide (KOH) in a single recipe. This creates a unique soap with properties of both bar soap and liquid soap - firm enough to hold its shape, yet soft and creamy with exceptional lather.
Why Make Dual Lye Soap?
- Superior lather: Creates rich, creamy, stable lather that's perfect for shaving or luxurious face/body bars
- Cream texture: Softer than bar soap, making it ideal for pressing into shaving bowls or tins
- Faster cure: The KOH portion cures quickly, reducing wait time to 2-4 weeks
- Customizable firmness: Adjust the NaOH:KOH ratio to get exactly the texture you want
Common Uses for Dual Lye Soap:
- Traditional shaving soap for brushes and bowls
- Cream bars for face washing
- Luxury body bars with extra-creamy lather
- Pet shampoo bars (easier to work into fur)
Understanding NaOH:KOH Ratios
The ratio of NaOH to KOH determines your soap's final texture and properties. Here's what to expect:
80% NaOH : 20% KOH
Mostly firm bar with slightly creamier lather. Good for body bars that need to hold up in a dish.
70% NaOH : 30% KOH
Cream bar consistency. Soft enough to press into containers, firm enough to slice. Popular starting point.
50% NaOH : 50% KOH (Recommended for Shaving Soap)
Classic shaving soap texture. Soft, pliable, incredible lather. Perfect for shaving bowls and tins.
40% NaOH : 60% KOH
Very soft cream soap. Must be stored in a container. Extra-quick lathering but won't hold bar shape.
30% NaOH : 70% KOH
Paste-like consistency, similar to liquid soap paste before dilution. Best for squeeze tubes or jars.
Step 1: Setting Up the Calculator for Dual Lye
The SoapMath calculator makes dual lye soap easy. Follow these steps:
1.1 Select Dual Lye Mode
In Step 1: Lye Selection, click on "Dual Lye (NaOH + KOH)" to enable the dual lye calculator.
When you select Dual Lye, new options will appear:
- An inline ratio display showing [textbox]% NaOH : [auto-calc]% KOH
- The percentages automatically adjust to total 100%
1.2 Set Your NaOH:KOH Ratio
Enter the NaOH percentage in the textbox. The KOH percentage calculates automatically.
For shaving soap:
Enter 50 in the NaOH field. This gives you 50% NaOH : 50% KOH.
For cream bars:
Enter 70 in the NaOH field. This gives you 70% NaOH : 30% KOH.
1.3 Adjust NaOH Purity
The calculator defaults to 100% NaOH purity. If your NaOH is lower purity (check the label), adjust accordingly.
Purity Note:
Most NaOH is 97-100% pure. KOH is typically 90% pure, but this is already factored into the calculator's SAP values. Only adjust the NaOH purity field.
Step 2: Formulating Your Recipe
2.1 Water Calculation
In Step 2: Water Calculation, select your preferred method. For dual lye soap:
- Lye Concentration 33-35% works well for most dual lye recipes
- Shaving soaps often use slightly less water (35-38% concentration) for a thicker paste
2.2 Superfat Settings
In Step 3: Superfat & Fragrance:
- Shaving soap: 3-5% superfat for optimal lather
- Cream face bars: 5-7% superfat for conditioning
- Luxury cream bars: 7-10% for extra moisturizing
Higher superfat reduces lather stability, so keep it lower for shaving soap.
2.3 Oil Weight
In Step 4: Oil Weight, enter your total oil weight. For a beginner batch:
- 300-500g for testing recipes
- 500-800g for shaving bowls/tins
- 1000g+ for full production batches
2.4 Optional: Additives & Colorants
In Step 5: Additives, Colorants & Water Replacements, you can enhance your dual lye soap:
Popular Shaving Soap Additives:
- Sodium Lactate (1-3%): Increases glide and slickness
- Bentonite Clay (1-2%): Improves razor glide and lather stability
- Kaolin Clay (1-2%): Silky feel, helps with slip
- Honey (1-2%): Adds moisturizing and lather boosting
Water Replacements:
Some soapmakers replace part of the water with goat milk, aloe vera, or tea for added benefits. For shaving soap, stick with distilled water to maximize lather.
Step 3: Selecting Oils for Dual Lye Soap
In Step 6: Oil Selection, build a recipe optimized for lather and cream. Dual lye soap excels when formulated with high-lather oils.
Classic Shaving Soap Recipe:
- Stearic Acid: 30-40% (creates dense, stable lather)
- Coconut Oil: 30-35% (big bubbly lather)
- Castor Oil: 10-15% (lather booster, slickness)
- Olive Oil: 10-15% (conditioning)
- Shea Butter: 5-10% (creaminess)
Cream Bar Recipe:
- Olive Oil: 30-40% (conditioning, creamy lather)
- Coconut Oil: 25-30% (lather)
- Shea Butter: 15-20% (creaminess, hardness)
- Castor Oil: 8-10% (lather boost)
- Avocado Oil: 5-10% (conditioning)
Stearic Acid Tip:
Stearic acid is key for shaving soap. It creates the dense, yogurt-like lather that shaving requires. It also speeds up trace significantly, so work quickly!
Step 4: Making Your Dual Lye Soap
Safety First:
- Wear safety goggles and gloves at all times
- Work in a well-ventilated area
- Have vinegar ready to neutralize any lye splashes
- Keep children and pets away
4.1 Prepare Your Lye Solutions
You have two options for mixing dual lye:
Option A: Combine Lyes First (Recommended)
- Weigh both NaOH and KOH into the same container
- Gently mix the dry lyes together
- Add the combined lyes to your measured water
- Stir until fully dissolved
Option B: Separate Solutions
- Split your water proportionally (same ratio as your lyes)
- Make separate NaOH and KOH solutions
- Cool both solutions
- Combine when adding to oils, or add separately
This method gives more control but is more complex.
4.2 Prepare Your Oils
- Weigh all oils and butters into your soap pot
- If using stearic acid, melt it first as it has a higher melting point
- Melt all solid oils on low heat
- Add liquid oils and stir to combine
- Allow to cool to 100-130°F (38-55°C)
4.3 Combine and Reach Trace
When oils and lye solution are both around 100-120°F:
- Slowly pour lye solution into oils while stirring
- Use a stick blender in short bursts (3-5 seconds on, stir manually, repeat)
- Watch for trace - dual lye often traces faster than regular soap
- Stearic acid accelerates trace significantly - be prepared to work quickly
Warning: Stearic acid + dual lye can trace in seconds. Have your mold ready before you start mixing!
4.4 Add Fragrance and Mold
- At light trace, add any clay or additives from Step 5 and mix well
- Add fragrance and colorant, mix thoroughly
- Pour/scoop into mold or press directly into shaving bowls
- Dual lye soap is thicker than bar soap batter - you may need to press it in
Step 5: Molding and Curing
5.1 Molding Options
- Shaving bowls/tins: Press directly into the container. The soap will conform and harden.
- Silicone molds: Great for cream bars. Flexible molds make unmolding easy.
- Jar/tub: For very soft ratios (40:60 or softer), pour into wide-mouth jars.
- PVC pipes: Create round pucks perfect for vintage-style shaving.
5.2 Unmolding
- Wait 24-48 hours before unmolding (longer for higher KOH ratios)
- Dual lye soap stays soft longer than bar soap - this is normal
- If too soft to unmold, wait another day or freeze briefly
5.3 Curing
Dual lye soap cures faster than pure NaOH soap:
- 50:50 or higher KOH: 2-3 weeks cure time
- 70:30 NaOH:KOH: 3-4 weeks cure time
- 80:20 or higher NaOH: 4-6 weeks, similar to bar soap
Tip: Cure shaving soap uncovered if possible - it hardens better with air circulation.
Troubleshooting Dual Lye Soap
| If you see this... | What's happening... | Solution |
|---|---|---|
| Soap traced too fast | Stearic acid accelerates trace; temperature too high; over-blended | Work cooler (100°F); have everything ready before mixing; use stick blender sparingly; skip stearic acid for slower trace |
| Soap is too soft after curing | KOH ratio too high; not enough cure time; too much liquid oils | Increase NaOH percentage (try 60:40 or 70:30); add more stearic acid; allow full cure time (2-4 weeks) |
| Lather is weak or thin | Not enough lather-boosting oils; superfat too high | Increase coconut oil to 35%; add more castor oil (15-20%); add stearic acid (30%+); reduce superfat to 3-5% |
| Soap cracked or is brittle | Too much stearic acid; unmolded too soon; not enough soft oils | Reduce stearic acid to 30-35%; wait longer before unmolding; add more liquid oils like olive or avocado |
| White residue on surface (soda ash) | Reaction with air during initial cure | Spray top with 91% isopropyl alcohol after pouring; cover mold with plastic wrap during first 24 hours; wipe off or steam to remove |
| Soap won't lather with brush | Not enough cure time; water too cold; brush not wet enough | Wait full cure time; use warm water; soak brush before loading; bloom soap surface with hot water for 30 seconds |
| Soap shrinks away from container | Normal water evaporation during cure | This is normal - cosmetic issue only; press soap back into container after cure if desired |
| Uneven texture or lumps | Stearic acid solidified unevenly; not mixed thoroughly | Keep oils warmer during mixing; blend more thoroughly; ensure stearic is fully melted before combining |