The selection of consumables for working with tanned leather is the foundation on which the durability of the entire product rests. Error in choice sewing thread can lead to the fact that even well-cut parts will come apart along the seam at the first load. Leather is a specific material: it is dense, does not stretch well and leaves puncture marks, so ordinary cotton threads are completely unsuitable here.
Unlike working with fabrics, where the elasticity of a seam is often more important than its strength, in leatherworking priority is given to wear resistance and the ability of the thread to withstand constant friction. If you take a thread that is too thin for thick leather, it will simply fray or burst under tension. Conversely, using a coarse cord for a thin chevro will ruin the appearance and make the seam hard and brittle.
There are several main types of threads, each of which has its own application characteristics. Professionals rarely use universal solutions, preferring to select materials for a specific project. In this article we will look at nylon threads (polyester) are considered the standard for most leather products due to their high tensile strength, but also consider waxed linen options for premium hand sewing.
Main types of threads for working with leather
The first thing the master faces is the choice between synthetic and natural materials. Synthetics dominate in industrial production and in the creation of products used in harsh conditions. Natural materials are often chosen for restoration or creating exclusive items in a vintage style.
Most Popular polyester threads, which are often called nylon. They are highly durable, do not rot, and are resistant to ultraviolet radiation and chemical influences. Their structure allows them to tighten tightly in the knot, which is critical for leather stitching. In addition, they are available in a huge range of colors, allowing you to choose the exact shade.
The second popular option is waxed linen. This is a classic saddle stitch. Linen threads are pre-impregnated with wax, which gives them rigidity and protects them from moisture. When the seam is tightened, the wax melts from friction and glues the fibers together, creating a monolithic structure. However, flax is less tensile than synthetics and can fray during prolonged contact with abrasives.
- 🧵 Nylon (Polyester): High strength, elasticity, rot resistance, ideal for machine and hand stitching.
- 🌿 Waxed linen: Traditional material for hand sewing, aesthetic appearance, requires skill to work, less durable.
- 🕸️ Kevlar: Extreme strength, used for special equipment, but difficult to work with and expensive.
- 🧶 Cotton with impregnation: Rarely used, only for decorative purposes or temporary seams, wears out quickly.
⚠️ Attention: Never use pure cotton without special impregnation for stitching loaded leather parts. The hygroscopicity of cotton will cause the thread to absorb moisture, swell, and then weaken as it dries, causing the seam to break.
Analysis of markings and sizing system
Understanding the labeling is key to making the right choice. Leatherworking uses different numbering systems and there is no room for confusion. Most often you can find the designations Tex, Denier (D) or simply the thread number (No.). The higher the number in the Tex system, the thicker the thread, whereas in some older numbering systems (eg LL) the logic may be reversed or not obvious.
System Tex (tex) shows the weight of 1000 meters of thread in grams. This is the most understandable and physically based system. If it says on the reel Tex 40, this means that 1 km of such thread weighs 40 grams. For comparison, thin lining threads may have Tex 15-20, and threads for sewing belts and saddles - Tex 70-100 and higher.
System Denier (Den) also indicates the weight, but already 9000 meters of thread. It is popular among manufacturers of nylon and nylon threads. To roughly convert Den to Tex, you need to divide the Den value by 9. For example, thread 140D will roughly correspond Tex 15.5.
Secrets of twisting threads
Unlike fabric sewing threads, which often have a Z-twist, leather threads (especially waxed ones) often have an S-twist. This is related to the direction of rotation of the needle or awl when hand sewing. If you use a thread with an inappropriate twist, it will fluff up as you work, rather than being pulled into a knot.
When purchasing, always pay attention to the number of folds. The thread can be single, double or triple. For machine stitching, twisted threads are usually used, which do not fluff at high speeds passing through the eye of the needle.
Correspondence table between thread and leather thickness
The correct ratio of the thickness of the material and the thread is the key to a neat seam. If the thread is too thin, it will “sink” into the puncture and the seam will be weak. If it is too thick, it will puff up, and the skin around the hole may become deformed or even tear when pulled together.
The table below shows approximate values for selecting threads depending on the thickness of the leather being processed. Please note that these values may vary depending on the density of the leather (hard vegetable tanned or soft chrome).
| Leather thickness(mm) | Product type | Recommended size (Tex) | Analogue (D/No.) |
|---|---|---|---|
| 0.5 – 0.8 | Haberdashery, light bags | 20 – 30 | 180D / №40 |
| 0.9 – 1.2 | Wallets, covers | 40 – 50 | 350D / №30 |
| 1.3 – 2.0 | Belts, sheaths, bags | 60 – 80 | 500D-700D / №20 |
| 2.5 – 4.0 | Saddle, heavy straps | 90 – 135 | 1000D+ / №10 |
For beginners, it is better to start with leather about 1.2–1.5 mm thick and thread Tex 50. This is the “golden mean”, which forgives small errors in tension and allows you to practice puncture and tightening techniques.
The main selection rule: the diameter of the thread in the stitched seam should be approximately 1/3 or 1/4 of the thickness of the leather. Visually, the seam should look harmonious, without sagging or rising above the surface.
Tools and preparation for sewing
Choosing threads is only half the battle. The second half depends on what you use to form the holes. Regular sewing needles with a sharp tip are absolutely not suitable for leather, as they cut the leather fibers, creating a cut that will turn into a crack under load.
Use special needle needles (for hand sewing) or needles with a triangular point (for machines). The awl pushes the leather fibers apart, maintaining their integrity, making the seam elastic and durable. To mark the puncture step, use a stepper or marker so that the holes are located at an equal distance from each other.
Before starting work, the thread needs to be prepared. If you are working with nylon thread, make sure that it does not have “memory” (does not curl in rings). If the thread curls, the seam will look untidy. Waxed threads sometimes require additional rubbing with wax (beeswax or special shoe wax) for better glide.
☑️ Preparation of the workplace
It is also important to thread correctly. When sewing by hand, the ends of the thread are often melted with a lighter, forming a hard tip that is easier to thread through an eyelet or a puncture. However, this must be done carefully so as not to create a too large ball that will get stuck in the hole.
Hand and machine stitching techniques
The stitching technique directly affects how the thread behaves in use. Considered the most durable for leather saddle stitch. Its peculiarity is that each hole is punched separately, and two threads pass through it (or one folded in half), which intersect inside the channel.
When machine stitching, a chain or lockstitch is used. Here it is critical to configure thread tension. If the tension is weak, the loop will not tighten at the surface of the skin, and the seam will be loose. If you overtighten, the leather may move like a boat, and the thread will constantly burst when the product is bent.
Sewing speed also matters. At high speeds, synthetic thread can overheat due to friction against the needle. This is especially true for thick threads (Tex 80+). In industrial settings, silicone emulsions are used to cool the needle; in home settings, they simply slow down.
⚠️ Attention: When stitching on a machine, never backtack (reverse) the leather. This will create a thickening that cannot be pierced with a needle again without damaging the material. Secure the thread only with knots or special seam clamps.
Product care and seam durability
Even the best threads require proper care. Synthetic threads require little to no maintenance, but the areas where the leather and thread meet can accumulate dirt. Regular cleaning of products with a soft brush will extend the life of the seams.
Waxed linen threads may lose wax over time, especially if the product is used in a warm environment. Periodically (once a year or as needed), the seams can be treated with leather conditioner or a light coat of wax. This will restore moisture-proof properties and prevent the fibers from drying out.
If you notice that the thread has begun to “fluff” or lose color, this is a signal that the material is being attacked. In the case of ultraviolet radiation, treatment with a spray with a UV filter will help. It is better to immediately carefully melt any mechanical damage to the thread (hooks) with a lighter to prevent further unraveling.
If the end of the thread sticks out and gets in the way after sewing, do not cut it at the root. Melt the tip with a lighter and quickly press it with a flat object (tweezers) to the skin. The molten ball will securely fix the knot and become invisible.
Frequently asked questions (FAQ)
Can I use regular #40 sewing thread on leather?
Theoretically, it is possible for very thin leather (0.3-0.5 mm) and products that do not bear load (for example, a decorative patch). However, for full-fledged leather products (wallets, belts) they are too weak and will quickly fray. It is better to use specialized nylon threads of appropriate thickness.
How to replace waxed thread if you don't have it on hand?
You can take a regular nylon thread (for example, for fishing tackle or special shoe thread) and wax it yourself. Pass the thread through a block of beeswax, pinch it between your fingers and pull so that the wax warms up and is absorbed into the structure of the thread.
Why does the thread constantly break when sewing on a machine?
There may be several reasons: the needle is too dull or thin (cuts the thread), incorrect tension setting, poor quality of the thread itself (uneven thickness) or too high a sewing speed, causing overheating. Check the needle and try reducing the speed.
Which thread is better for a belt: nylon or flax?
For a belt that will be worn daily and experience tensile loads, it is definitely better to choose high-strength nylon (polyester) (Tex 70-90). Linen is more aesthetically beautiful when cut, but it is less durable under constant dynamic load and contact with sweat and moisture.