Soap-Making Methods Explained: Melt & Pour, Cold Process, and Hot Process
When shopping for handcrafted soap bars (not liquid cleansers), you’ll often see makers reference how a bar was made: Melt & Pour (MP), Cold Process (CP), or Hot Process (HP).
All three methods can produce excellent soap — but they differ in ingredients, process, cure time, and visual behavior. This guide breaks down those differences clearly and factually, so you know what you’re holding in your hand and why it behaves the way it does.
At a glance: three soap-making methods
- Melt & Pour (MP) – Soap is made from a pre-formulated base that is melted, customized, and poured into molds.
- Cold Process (CP) – Soap is made from scratch using oils/fats and sodium hydroxide (lye), then cured for several weeks.
- Hot Process (HP) – Similar to cold process, but cooked with heat to complete saponification more quickly.
This article focuses on solid soap bars made with sodium hydroxide. Liquid soaps and cleansers typically use potassium hydroxide and behave very differently.
Melt & Pour Soap (MP)
What it is
Melt & Pour soap starts with a fully saponified soap base created by a manufacturer. That base is melted down, then customized with colorants, additives, and fragrance before being poured into molds to set.
Important note: not all melt & pour bases are equal. Some are true soap (made from oils + lye), while others lean more toward detergent-based formulations. Quality depends on the base itself — not the method.
What customers may notice
- Can be crystal-clear or completely opaque
- May look similar to cold process when natural powders and clays are used
- Smooth edges and consistent shapes
- Ready to use once fully cooled and hardened
About glycerin (and “sweating”)
Melt & pour soap naturally contains a high level of glycerin, a humectant that attracts moisture from the air. That’s why MP bars are best stored wrapped until use.
If you ever see glycerin dew (tiny beads or a crystalline film on the surface), it’s purely cosmetic. Once the bar is used and rinsed, it disappears.
Color behavior
Natural colorants can shift in MP soap due to pH, just as they can in cold process. For example, sweet potato powder may appear bright fuchsia as a dry powder, but can turn grayish or blue-toned once incorporated into a soap base.
Shop this bar:
Saffron Twist – Small Batch Chamomile + Aloe Soap
Shop this bar:
Tiny Escapes – Small Batch Soap Bars
Cold Process Soap (CP)
What it is
Cold Process soap is made from scratch by combining oils or fats with a sodium hydroxide solution. This triggers saponification — the chemical reaction that turns oils and lye into soap and glycerin.
Once poured into molds, CP soap needs time to cure, typically 4–6 weeks.
Why curing matters
Curing serves two purposes:
- Water evaporation – creates a harder bar that lasts longer in use
- Honest weight – prevents overcharging by selling a bar before excess water has evaporated
Even though soap is safe to use once saponification is complete, curing ensures that a bar sold as 5 oz doesn’t shrink to 4 oz later.
Ingredients & fats
Cold process offers full control over the recipe. Common fats include:
- Plant oils (olive, coconut, etc.)
- Beef tallow
- Lard (pork fat) — increasingly popular for its creamy lather and sustainability
Color behavior
Natural colorants in CP soap can fade, deepen, or shift over time. This is normal and tied to pH, light exposure, and curing, not to the quality of the soap.
Shop this bar:
Tallow + Lavender – Beef Tallow Soap
Shop this bar:
Lavender Lemongrass – Olive & Coconut Oil Soap
Hot Process Soap (HP)
What it is
Hot Process soap uses a similar recipe to cold process — oils/fats plus sodium hydroxide — but the mixture is cooked with heat. This accelerates saponification before the soap is molded.
What customers may notice
- A more rustic, textured appearance
- Less intricate swirls than CP
- Bars are often usable sooner, though many makers still allow a short cure for best results
Hot process soap is still “real soap” in every sense; the main difference is when saponification happens.
A quick note on “soap” vs. “beauty bars”
Not everything sold as “soap” is actually soap.
Many mass-market bars are synthetic detergent bars (often called syndet or beauty bars). These are not inherently bad — in fact, they can be excellent for specific uses like shampoo or facial cleansing — but they are chemically different from true soap made with oils and lye.
At Panta Rei Made, true soap bars and syndet-based bars are labeled and formulated intentionally, depending on the purpose of the product.
How to choose what’s right for you
Rather than focusing on the method alone, consider:
- Ingredients – oils, fats, clays, botanicals, or detergents
- Skin feel – creamy, bubbly, conditioning, or clarifying
- Longevity – how long a bar lasts in your shower
- Aesthetic – smooth, rustic, translucent, or heavily textured
All three methods — MP, CP, and HP — can be thoughtfully made and high quality when done with care.