Glossary
The world of DIY personal care comes with its own vocabulary. Some of it is chemistry, some of it is cosmetic industry shorthand, and some of it is just words that appear on ingredient labels without explanation. This glossary covers the terms used across Batch and Bubble recipes and guides with plain language definitions written for makers, not scientists.
If you encounter a term in an article that isn’t here, get in touch and I’ll add it.
A
Active concentration The percentage of a raw ingredient that is the biologically active compound, as opposed to the carrier or solvent it’s supplied in. D-panthenol, for example, is supplied at 75% active concentration — meaning 75% of the liquid is the active panthenol and 25% is water. When calculating how much active ingredient is in your formula, you multiply the usage rate by the active concentration.
AICS (Australian Inventory of Chemical Substances) The official Australian register of chemicals approved for industrial and commercial use. An ingredient listed on the AICS is approved for use in Australia. Relevant when sourcing cosmetic ingredients and verifying their regulatory status.
Alkaline Having a pH above 7. The opposite of acidic. Traditional soap-based shampoo bars are alkaline, sitting at pH 9 to 10. Hair and scalp prefer a slightly acidic environment (pH 4.5 to 5.5), which is why high-pH products can cause frizz and cuticle disruption.
Amphoteric An ingredient that carries both positive and negative electrical charges depending on the pH of the solution it’s in. CAPB (cocamidopropyl betaine) is an amphoteric surfactant — this dual charge makes it compatible with most other cosmetic ingredients and contributes to its mildness.
Anhydrous Containing no water. An anhydrous formula is one in which no free water is present in the finished product. Syndet shampoo and conditioner bars are anhydrous, which is why they don’t require a preservative — bacteria and mould need water to survive.
Anionic Carrying a negative electrical charge. Anionic surfactants like SLS (sodium lauryl sulphate) are effective cleansers but can be irritating at higher concentrations. The term is relevant when understanding how different surfactants interact with hair, which carries a slight negative charge when clean.
B
Batch weight The total weight of all ingredients in a single making session. In a 531g batch of shampoo bars, 531g is the batch weight. Knowing your batch weight allows you to scale recipes up or down accurately by keeping ingredient percentages consistent.
Broad-spectrum preservative A preservative that protects against a wide range of microorganisms — bacteria, yeast, and mould — rather than targeting only one type. Any cosmetic product containing water requires a broad-spectrum preservative. Anhydrous products like solid bars do not.
BTMS-25 / BTMS-50 Both are conditioning emulsifiers used in conditioner bars and hair care products. The number refers to the active concentration of behentrimonium methosulfate — 25% in BTMS-25 and 50% in BTMS-50. BTMS-50 is firmer and more concentrated, making it the standard choice for solid conditioner bar formulation. BTMS-25 produces a lighter, softer result and is more commonly used in liquid or cream conditioners.
C
CAPB (cocamidopropyl betaine) A mild amphoteric surfactant derived from coconut oil, used as a secondary surfactant in syndet shampoo bars. It boosts lather, adds mildness to the formula, and helps bring ingredients together during mixing. At 30% active concentration, it is supplied as a liquid.
CAS number A unique numerical identifier assigned to every chemical substance by the Chemical Abstracts Service. CAS numbers appear on safety data sheets and ingredient specifications and allow you to verify exactly which substance you’re working with regardless of the trade name used by a supplier.
Cationic Carrying a positive electrical charge. BTMS-50 is a cationic conditioning emulsifier. Hair carries a slight negative charge, which means cationic ingredients are attracted to and bind with the hair shaft — this is the mechanism by which BTMS-50 conditions hair rather than simply coating it.
Cetyl alcohol A fatty alcohol (not a drying alcohol) derived from coconut or palm oil. Used in both shampoo and conditioner bars as a hardening agent and emollient. Despite the name, it contains no ethanol and does not dry the hair or skin. It appears as small white waxy pellets at room temperature.
Cold process soap A method of making soap by combining lye (sodium hydroxide) with oils or fats. The chemical reaction between lye and oils — called saponification — produces soap and glycerine. Cold process soap bars have a naturally high pH (9 to 10) and require a curing period of four to six weeks. The bars on this site are not cold process soap.
Cosmetic grade A level of purity appropriate for ingredients applied to skin and hair. Cosmetic grade ingredients are manufactured and tested to standards that make them safe for personal care use. When sourcing ingredients for home formulation, always use cosmetic grade rather than industrial or food grade equivalents.
Cure / curing period The time allowed after making a bar before it’s ready to use. For syndet bars, the cure period is seven days — primarily to allow the bar to harden fully and any residual moisture to evaporate. For cold process soap bars, the cure period is four to six weeks, during which saponification completes and pH stabilises.
D
D-panthenol The biologically active form of panthenol (provitamin B5). The “d-” refers to the specific molecular orientation that makes it active in hair and skin. L-panthenol, the mirror-image form, has no meaningful biological activity. D-panthenol penetrates the hair shaft and converts to pantothenic acid, improving moisture retention and elasticity from within.
Double boiler A two-vessel heating setup used to melt ingredients gently without direct heat. A glass bowl sits over a saucepan of simmering water — the steam heats the bowl from below without the risk of overheating sensitive ingredients. Used in both shampoo and conditioner bar making for the melt phase.
E
Emollient An ingredient that softens and smooths the skin or hair surface. Emollients work by filling gaps in the cuticle or skin barrier, reducing moisture loss and improving texture. Cetyl alcohol, shea butter, and jojoba oil are all emollients used in the Batch and Bubble conditioner bar formula.
Emulsifier An ingredient that allows two substances that wouldn’t normally mix — typically oil and water — to combine and stay combined. BTMS-50 is a conditioning emulsifier, meaning it emulsifies while also conditioning the hair. In anhydrous bar formulas, the emulsifying properties of BTMS-50 help the ingredients bind together into a stable solid.
F
Fatty acid A type of organic acid found in fats and oils, composed of a carbon chain with a carboxylic acid group at one end. Fatty acids determine many of the properties of an oil or butter — their chain length and saturation level affect whether an ingredient is liquid or solid at room temperature, how it feels on hair or skin, and how shelf-stable it is. Shea butter is high in stearic and oleic fatty acids.
Fatty alcohol A type of alcohol derived from fatty acids — plant or animal fats — with a long carbon chain. Unlike short-chain alcohols like ethanol (which is drying and volatile), fatty alcohols are solid at room temperature, non-drying, and have emollient properties. Cetyl alcohol and stearyl alcohol are examples commonly used in hair and skin care.
H
Hair cuticle The outermost layer of the hair shaft, made up of overlapping scales arranged like roof tiles. When the cuticle lies flat, hair looks smooth and shiny and retains moisture well. When the cuticle is raised — by alkaline products, heat damage, or mechanical friction — hair looks dull, feels rough, and loses moisture more easily. Many conditioning ingredients work by closing or smoothing the cuticle.
Hair shaft The visible part of a strand of hair — the portion above the scalp. The hair shaft is composed of three layers: the medulla (innermost), the cortex (middle, where most of the hair’s strength and colour lives), and the cuticle (outer protective layer). Conditioning ingredients target the cuticle and, in the case of smaller molecules like d-panthenol, penetrate into the cortex.
Hard water Water with a high concentration of dissolved minerals, primarily calcium and magnesium. Hard water interferes with the lathering of soap-based shampoo bars by binding to soap molecules and forming a waxy scum. Syndet bars are significantly less affected by hard water. Signs of hard water include white mineral deposits on taps and shower screens.
Humectant An ingredient that attracts and retains moisture from the surrounding environment. Humectants draw water molecules toward themselves — in hair care, this means drawing moisture toward the hair shaft. Glycerine and d-panthenol are both humectants used in the Batch and Bubble conditioner bar. In very dry climates, humectants can draw moisture from the hair rather than the air, so they work best in moderate to humid conditions.
Hygroscopic The property of attracting and absorbing moisture from the surrounding air. Glycerine is hygroscopic, which is why bars containing it can develop a slight surface tackiness in humid climates like Brisbane over time. The same property that causes surface tackiness is what makes glycerine useful as a humectant in the formula.
I
INCI name International Nomenclature of Cosmetic Ingredients — the standardised international naming system for cosmetic ingredients. INCI names appear on product labels and in safety data sheets and allow you to identify an ingredient regardless of the trade name a supplier uses. Sodium cocoyl isethionate is the INCI name for SCI, for example.
K
Keratin The primary protein that makes up hair, skin, and nails. Hair is approximately 95% keratin. Many conditioning ingredients work by interacting with keratin — d-panthenol binds to keratin proteins and improves their moisture retention. Damage to keratin (from heat, chemical processing, or mechanical stress) is what makes hair feel rough, look dull, and break more easily.
L
Leave-on vs rinse-off A distinction in how a product is used that affects formulation requirements. Leave-on products (serums, oils, leave-in conditioners) remain on the hair or skin after application. Rinse-off products (shampoos, conditioners, body wash) are washed away after a short contact time. Usage rates for active ingredients like d-panthenol differ between leave-on and rinse-off applications — leave-on products typically use higher concentrations because the ingredient has more time to act.
Limescale The white, chalky mineral deposit left by hard water on surfaces including taps, shower screens, and kettles. Limescale is composed primarily of calcium carbonate and is a visible indicator of water hardness. The same minerals that form limescale on surfaces form a waxy film on hair when soap-based shampoo bars are used in hard water.
Lye (sodium hydroxide) A strongly caustic alkali used in cold process soap making. Lye reacts with oils in a process called saponification to produce soap. It requires careful handling — goggles, caustic-rated gloves, and dedicated equipment — because it causes serious burns on contact with skin. The bars on this site do not use lye.
M
Melt phase The first stage of making a syndet bar, during which solid ingredients are melted together using a double boiler. The melt phase produces a liquid mixture of the primary ingredients that is then combined with the second phase before being poured into moulds.
Mineral deposits Accumulations of calcium, magnesium, and other minerals from hard water on surfaces or hair. In hair, mineral deposits roughen the cuticle, reduce lather quality, and contribute to the waxy, heavy feeling that makes shampoo bars seem ineffective. An apple cider vinegar rinse dissolves mineral deposits effectively.
P
Patch test A simple safety test performed before using a new product on the full area of application. A small amount of product is applied to a discreet area of skin (typically the inner forearm or behind the ear) and left for 24 to 48 hours to check for any reaction. Recommended when trying any new formula, particularly for those with sensitive skin or known ingredient sensitivities.
pH A scale from 0 to 14 that measures how acidic or alkaline a substance is. A pH of 7 is neutral (pure water). Below 7 is acidic, above 7 is alkaline. Hair and scalp prefer a slightly acidic environment of pH 4.5 to 5.5. Traditional soap bars sit at pH 9 to 10, which can disrupt the hair cuticle. Syndet bars are formulated to sit much closer to the hair’s natural pH.
Provitamin A substance that is converted into a vitamin within the body or, in the case of topical applications, within the tissue it’s applied to. D-panthenol is a provitamin — it’s converted to pantothenic acid (vitamin B5) within the hair shaft. Using the provitamin rather than the vitamin directly allows it to penetrate the hair shaft more effectively before converting.
R
Rinse-off See Leave-on vs rinse-off.
S
Safety Data Sheet (SDS) A standardised document provided by ingredient suppliers that details the properties, hazards, safe handling requirements, and emergency procedures for a chemical substance. SDS documents are publicly available from reputable cosmetic ingredient suppliers and are worth reading for any ingredient you’re working with for the first time. They confirm the ingredient’s grade, purity, identified hazards, and regulatory status.
Saponification The chemical reaction between lye (sodium hydroxide) and oils or fats that produces soap and glycerine. Saponification is the basis of cold process soap making. Syndet bars do not involve saponification — they use a melt-and-mix process instead.
Scalp recalibration The process by which the scalp adjusts its oil (sebum) production after switching to a gentler cleanser. Conventional shampoos containing sulphates strip the scalp aggressively, causing it to overproduce oil to compensate. When switching to a syndet bar, the scalp continues producing oil at the old rate for a few weeks before registering that less stripping is occurring and reducing production accordingly. This is the primary cause of the greasy roots many people experience during the shampoo bar transition period.
SCI (sodium cocoyl isethionate) The primary surfactant in Batch and Bubble syndet shampoo bars. Derived from coconut oil, SCI is one of the gentlest cleansing surfactants available for solid bar formulation. It produces a rich, creamy lather, has a naturally mild pH, and is significantly less reactive with hard water than soap-based surfactants. Available in chip, flake, or powder form.
SDS See Safety Data Sheet.
Sebum The natural oil produced by sebaceous glands in the scalp. Sebum protects the scalp and hair shaft, provides moisture, and creates the scalp’s slightly acidic environment. Overcleansing strips sebum, prompting the scalp to produce more. Undercleansing allows sebum to accumulate, making hair look and feel greasy.
Second phase The mixture of ingredients that is combined with the melted first phase during bar making. In the conditioner bar recipe, the second phase contains glycerine, d-panthenol, and kaolin clay. It is prepared separately at room temperature and added to the first phase once it has cooled to the appropriate temperature.
Silicone buildup The accumulation of silicone residue on the hair shaft from conventional conditioners and styling products. Silicones coat the hair to create artificial smoothness and shine but don’t wash out easily with gentle cleansers. Switching to a syndet bar can cause a temporary period where existing silicone buildup makes hair feel heavy or coated — this clears over two to four weeks. An apple cider vinegar rinse accelerates the process.
Soft water Water with a low concentration of dissolved minerals. Soap-based shampoo bars lather freely and rinse cleanly in soft water. If you’ve tried a shampoo bar while travelling and had a completely different experience than at home, water hardness is most likely the reason.
Sulphates (SLS / SLES) Sodium lauryl sulphate and sodium laureth sulphate — anionic surfactants used as primary cleansers in many conventional shampoos. Highly effective at producing lather and removing oil, but associated with scalp irritation and stripping at higher concentrations. The syndet bars on this site use SCI rather than sulphates.
Superfatting A soap-making technique in which a small excess of oil or fat is left unsaponified in the finished bar, producing a milder, more moisturising result. Relevant to cold process soap making rather than syndet bars, but worth knowing as a term that appears frequently in broader soap-making communities.
Surface tension The tendency of a liquid’s surface to resist disruption, caused by cohesive forces between liquid molecules. Surfactants reduce the surface tension of water, allowing it to mix with oils and form the lather that makes cleansing possible.
Surfactant Short for surface-active agent. A compound that reduces the surface tension between two substances — typically oil and water — allowing them to mix. Surfactants are the cleansing ingredients in shampoos and body washes. They surround oil molecules and allow them to be rinsed away with water. SCI and CAPB are both surfactants used in the Batch and Bubble shampoo bar formula.
Syndet bar Short for synthetic detergent bar. A solid cleansing or conditioning bar built around surfactants or conditioning emulsifiers rather than soap. Syndet bars are lye-free, have a naturally mild pH, perform better in hard water than soap-based bars, and require a shorter curing period. All bars on this site are syndet bars.
T
Tare To zero a digital scale with a container already on it, so that subsequent measurements reflect only the ingredient being added rather than the weight of the container. Essential for accurate ingredient measurement in bar making. Most digital scales have a dedicated tare button.
Transition period The adjustment phase experienced by the scalp when switching from conventional sulphate-based shampoo to a syndet bar. The scalp continues producing oil at its previous elevated rate for two to six weeks before recalibrating to a lower baseline. During this time hair may feel greasy, heavy, or different from usual. The transition is temporary and resolves on its own.
U
Unsaponifiables The fraction of an oil or butter that does not react with lye during saponification and therefore remains in its original form in a finished soap. Shea butter is notable for its relatively high unsaponifiable content, which includes tocopherols, phytosterols, and other compounds associated with its emollient and protective properties.
Usage rate The recommended percentage at which an ingredient should be included in a formula. Usage rates are provided by ingredient suppliers and are based on safety testing and efficacy data. Working within recommended usage rates is important both for safety and for achieving the intended result.
W
Water activity A measure of the availability of free water in a product to support microbial growth. A product with low water activity — like an anhydrous bar — does not provide the conditions necessary for bacteria, yeast, or mould to survive. This is why syndet bars do not require a preservative.
Wax ester The molecular structure of jojoba oil — technically a liquid wax rather than a true oil. Wax esters are more resistant to oxidation than the triglycerides found in most vegetable oils, giving jojoba a shelf life of several years compared to the one to two years typical of most carrier oils.
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Written by Neets at Batch and Bubble
DIY personal bathroom care recipes for real life
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