There are two main methods of soap making: cold process (CP), and hot process (HP). So what is the difference between cold process vs hot process soap? And which should you make? 

Cold process vs hot process soap

Both cold process and hot process soap bars are produced via a chemical process called saponification, a reaction between triglyceride and lye. This creates glycerin (glycerol), and a salt of fatty acids, which is soap.

Both types of soap can be made from different fats (for example, plant oil, plant butter or animal fat) and a strong alkali, also called ‘lye’.

As the name suggests, the main difference between cold process vs hot process soap is that hot process soap is made at higher temperatures than cold process soap. Cold process soap is made at relatively low temperatures (usually 30-50°C), while hot process soap is made at higher temperatures (usually 50-100°C). This affects the soap making method as well as the properties of the finished soap.

Cold process vs hot process soap: A quick guide Soapmaking

Key differences between cold process vs hot process soap making

Some of the key difference between the two types of soap making are:

1. Temperature 

Cold process soap is made at relatively low temperatures (usually 30-50°C), while hot process soap (as the name suggests)  is made at higher temperatures (usually 50-100°C).

2. Saponification 

In hot process soapmaking the saponification happens during the soap making process while the soap is ‘cooking’ in a slow cooker. In cold process soap, saponification occurs in the mold. 

3. Equipment

Cold process and hot process soap making use the same basic equipment – lye-safe containers, stick (immersion) blender, whisk, spatula, thermometer, soap mold. One key difference is that in hot process soap making a slow cooker (or crock pot) is very helpful. This is used to ‘cook’ the oil mixture while it saponifies. Using a slow cooker/crock pot ensures the soap mixture does not overheat and that the temperature remains fairly constant.

4. Post-cook superfat

Superfat is ‘extra fat’ that does not react with the lye and turn into soap. It is a portion of fat (oils, butters) that is added to make the finished bars more nourishing. In hot process soap the superfat is added after the saponification is complete, which means you can control which oil or butter is your ‘superfat’ and therefore the extra nourishing properties your soap will have. In cold process soapmaking, the superfat is made of all of the oils in the recipe.

5. Time to make

In hot process soap making, especially if working at high temperatures, the whole process can be very quick, even 30 minutes from start to finish. 

6. Cure time

In cold process soap making you need to wait four to six weeks for your soap to cure before you can use it. Hot process soap bars can be used straight away since the saponification is finished before the soap is poured into the mold. However, a couple of weeks of cure time will still benefit the soap.

7. Skill level

Beginners should start by making cold process soap. To ensure you make soap correctly and safely we recommend taking a detailed and reliable class such as School of Natural Skincare’s Cold Process Soapmaking course.

As it takes place at higher temperatures, hot process soap making requires more skill and should only be carried out once you are comfortable with cold process soap making. Make sure you follow a comprehensive and reliable guide, such as our Hot Process Soapmaking class.

Cold process vs hot process soap: A quick guide Soapmaking

At a glance: Cold process vs hot process soap

Cold process Hot process
Skill level Suitable for beginners Suitable for those experienced in cold process soapmaking
Temperature Made at 30-50°C Made at 50-100°C
Equipment Lye-safe containers, stick (immersion) blender, whisk, spatula, thermometer, soap mold, safety equipment (rubber gloves, protective clothing, goggles) The same as cold process, plus a slow cooker/crock pot
Saponification Occurs in the mold Occurs during the cooking stage
Post-cook superfat Superfat is made of all of the oils in the recipe We can control which oils are added as the superfat oils
Unmolding Usually 48-72 hours after pouring Can be unmolded within a day
Cutting Soon after unmolding Cut straight after unmolding
Curing Needs to cure for four to six weeks before use Soap can be used as soon as it is cut, though it does benefit from curing (4 weeks)
Soda ash Can develop soda ash Never develops soda ash
Appearance Smooth appearance, usually light, creamy color Deeper, darker color; rustic appearance
Swirls Elaborate swirls and many different swirl techniques are possible Only very simple swirls are possible
Water content Various, from 25-38% (water as a percentage of oils) Keep the total water content (water as a percentage of oils) between 30% and 38%
Acceleration, ricing, separation, cracking Can occur when using unsuitable/accelerating fragrances or when soap overheats in the mold Does not occur
Clean up  Laborious as utensils are still coated with a high amount of unsaponified oils Easy
Cold process vs hot process soap: A quick guide Soapmaking

Learn more in our online Cold Process and Hot Process Soap Making classes

Cold process soap making is the ideal place to start if you are new to soap making. With our comprehensive, online Cold Process Soap Making class, you’ll be making gorgeous soaps in a matter of days. 

If you have already made at least a few batches of cold process soap and would like to learn how to make hot process soap we have the perfect class for you!

Advanced soapmaking: Hot Process Soap is a detailed class that covers everything you need to know to make hot process soap safely and successfully. Containing two detailed step-by step videos showing you exactly how to make both low temperature and high temperature hot process soap (plus what to do in the case of a ‘soap volcano’!), a beautiful and detailed class textbook to download, tried-and-tested recipes to follow and tutor support from a master soapmaker, you’ll have everything you to need to create exceptional hot process soap. 

This advanced class can be found inside our Natural Cosmetic Formulation Club. Join now for immediate access to the class, or if you are already a member head over to the Classes dashboard to get started. Please note: As this is an advanced class we recommend that you only take it once you are confident in your ability to make cold process soap. Here’s a sneak peek at the class contents:

  1. Introduction To Hot Process (HP) Soapmaking
  • Benefits of hot process soapmaking
  • Differences between hot and cold process soapmaking
  • Mandatory safety information
  • Soapmaking terminology
  1. Making Hot Process Soap
  • Low temperature vs high temperature hot process soapmaking
  • Hot process soapmaking overview
  • The soapmaking process: hot process soap (low temperature)
  • The soapmaking process: hot process soap (high temperature)
    1. Variations On The Hot Process Soapmaking Method
    • Fluid hot process soap
    • Making hot process soap without a slow cooker
    1. Hot Process Soap Recipes
    • Basic Nourishing Soap with Shea Butter
    • Cocoa Butter Soap
    • Oatmeal Honey Soap
    • Milk and Yogurt Soap

    Join the Natural Cosmetic Formulation Club today! 

    Check out our Natural Cosmetic Formulation Club to find out how you can join the Club, get access to Advanced soapmaking: Hot Process Soap and discover more exciting classes.

    If you have any questions, please email us at hello@schoolofnaturalskincare.com

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