Soft Leather: How to Specify Softness, Not Just Ask for It

Every brief asks for soft leather. Few say how soft, measured how, on which part of the hide. That gap is where bulk stops feeling like the sample.

A guide by TL San Martín, a tannery of origin in Elda (Alicante, Spain) since 1995, LWG Gold certified under the Leather Manufacturer standard.

TL San Martín tans and finishes leather in Elda, Spain, since 1995, certified LWG Gold under the Leather Manufacturer standard (how to check that is in how to read an LWG certificate). B2B accounts can order colour cards and swatch books free, up to 12 cards per order, in 3–5 days. We get asked for "soft leather" more than for any other quality, and the word means something different to every designer who uses it.

What makes leather soft?

Softness is built in at five points, and a tannery can turn each one up or down:

1. The animal and its age. Lamb, kid goat and young calf have finer, looser fibre structures than mature cattle. Hair-sheep and lamb skins are soft before anyone touches them.
2. The tannage. Chrome tanning gives a more supple, stretchier leather than vegetable tanning, which tends to fill and firm the fibres. Most soft leathers are chrome-tanned or chrome-free with a synthetic system designed for softness.
3. Retanning and fatliquoring. Fatliquors are oils worked into the wet leather to lubricate the fibres so they slide instead of locking when the leather dries. This is the main softness lever in the drum.
4. Mechanical work. Staking flexes the dry leather over pins to break the fibre bonds; milling tumbles it dry in a drum for hours. Milling gives the heaviest, most relaxed hand and usually a slightly pebbled grain.
5. The finish. Every coat of pigment and top-coat adds stiffness. The softest leathers carry the least finish, which is also why they mark more easily.

Thickness matters as well: the same leather split at 0.8 mm feels much softer than at 1.4 mm. If you are choosing a thickness for footwear, see leather thickness for shoe uppers first.

Which leathers are the softest?

"Nappa" began as a glove leather from lamb skins and is now a trade name for any soft, full-grain leather, from any animal. Ask what species and thickness sit behind it. For apparel specifically, garment leather: how to choose lambskin goes deeper. For goat, see goat leather from a Spanish tannery.

Is soft leather the same as smooth leather?

No. Smooth describes the surface: a closed, even grain without a printed or embossed pattern. Soft describes the hand: how the leather bends and drapes. A box calf is smooth and firm; a milled cow is soft with a pebbled grain; a sheep nappa is usually both. If you are unsure what a "smooth" offer really is, check whether it is full grain or corrected, explained in full grain, corrected grain and split.

How is leather softness measured?

With ISO 17235 (also published as IULTCS/IUP 36). A clamped piece of leather is pressed by a rod of fixed load through a ring; the gauge reads how far the leather distends, in millimetres. A higher reading means a softer leather. The test is non-destructive, so it can be done on a full hide at goods-in.

Three things to know before you write a number down:

• There is no official "soft" value per product. The standard defines the method, not pass marks. Your target has to come from a leather you have approved.
• Readings depend on the ring size and on thickness. Compare only readings taken with the same ring, on leathers of the same thickness range.
• Readings vary across the hide. The belly is softer than the back. Take the reading at the position set in ISO 2418 and after conditioning to ISO 2419, or the numbers will not be comparable.

What does softness cost in performance?

Softer usually means weaker and stretchier. The same oils and milling that relax the fibres lower tear strength, so ask for a tear result (ISO 3377-2) alongside the softness reading. In bags, a very soft leather needs a fused backing or reinforcement at handles and stress points. In shoes, an upper that is too soft can wrinkle at lasting and lose shape across the vamp; it needs the right lining and counter. Softer finishes also show scratches sooner, which is a design choice, not a defect.

How do you put softness into a spec?

Turn the word into a line your supplier can commit to:

1. Base article, species and thickness with tolerance (e.g. 0.9–1.1 mm).
2. Softness target from your approved sample: ISO 17235 reading, ring size, and a tolerance you agree with the tannery.
3. Sampling position and conditioning: ISO 2418 and ISO 2419.
4. Minimum tear load (ISO 3377-2) so softness is not bought at the price of strength.
5. Finish level: aniline, semi-aniline or pigmented, and gloss.
6. A physical reference kept by both sides.

Then check that the lines appear in the supplier's data sheet with a value, tolerance and method: see which lines of a technical data sheet bind a supplier. Hand varies between batches like colour does, for the reasons in why bulk leather doesn't match the sample.

Which leathers to sample for this use?

From our library, Monaco (hair-sheep nappa, 0.8–1.0 mm, in stock) and Irimatto (sheep nappa, 0.8–1.0 mm, seasonal collection) are the starting points for soft garments, linings and small leather goods. For product-led ranges, browse leather for garments, leather for handbags and leather for small leather goods, then request samples in the thickness you would order.

Post on the Business Board, TL San Martín's open, free B2B board for the leather and footwear trade. Use Materials to describe the leather you need (species, thickness, hand, quantity), or Partners & factories to find a maker that already works with soft leathers. Tanneries, factories and designers reply directly.

TL San Martín tans and finishes leather in Elda, Alicante, since 1995: LWG Gold under the Leather Manufacturer standard — the only standard under which a Gold medal exists at all; a Trader tops out at “Approved”. Request samples before you specify anything.