Report July 2025

We were at production again this month, and visited farmers to see this year’s crop – fact-finding, discussing, negotiating, etc. Learning. Because my role has increased to become the lead engineer for our Japanese manufacturing partner, while they’ve added a very experienced jute projects advisor from an Osaka-based competitor to liaise with on our developments.

Opinion must alter based on continually improving information. Even at the heart of jute farming, details are easily misunderstood. Confusion continually arises. This is in part due to literacy, varying local terminologies, Bengali pronunciation, how things are done for markets irrelevant to ours, no understanding of what fibre will be used for, and from limited published data not in step with hard realities on the ground. For example, the Bangla BT raw jute grading system is not what the farmer cooperative syndicate Kutchas and yarn mill procurement managers use. Nor have they even heard of it.

This month, let’s delve into product tenacity, where the strength to twist ratio combines coherence and obliquity. Because cabled (twisted, as opposed to braided) rope is made from twisted yarns, counter-twisted to strands, and finally twisted to lock the 3-dynamics together, in addition to the raw material quality, the initial yarn twist ratio will have an impact on strength and stability.

There are two main yarn twists – warp and weft. Weft yarns are used in weaving, eg. Hessian cloth, where they need to be flexible enough to run in and out crosswise perpendicular to stronger, often heavier warp yarns. Weft yarns are generally twisted looser, and are inherently weaker. Not recommended for making rope required to take longitudinal load.

Business practise where jute is grown and made to yarn, especially with low volume orders (under 100 tonnes) means supply is often with whatever might be available. Export 5 tonne minimum order quantity is always on Sale-No-Return terms. Therefore, purchasing direct from the farm cooperative syndicates and making yarn ourselves brings a big advantage, because we can get exactly the quality we want, reliably, and at better prices.

Jute yarns can be produced in a range of diameters specified in Imperial Pounds per 14,400 Yards weight, commonly between 6 and 28lb (blame The East India Company and British Raj). Spinning is always single-ply, and can be combined by twisting into multiple-plies for use in strings and twines where plying produces the middle counter-twist dynamic.

While jute fibre has high tensile strength, it also has relatively low elongation at break, meaning it withstands significant force before breaking, but doesn’t stretch much before fracturing. It’s a plant fibre. Not homogenous. The strongest structure is where all sections of the yarn are composed of filaments from the same part of the same plant. Thus, their specific growth construction means they share same tiny elasticity, and therefore better support each other in parallel.

As an example, two 7.5lb yarns can be 2-ply (counter-twisted together) to make up a total theoretic 15lb (15/2). But separate forces act to weaken the overall strength. Filaments from each yarn will almost certainly come from different plants, probably from different fields, maybe even different growing areas with different seasonal conditions, etc. If separate filaments elongate more than others around them they can fracture more readily, and overall strength diminished.

Secondly, two 7.5lb yarns themselves can be slightly different, eg. count variation (effectively, diameter tolerance), etc. Finally, twisting fibre into yarn, counter-twisting to multiple-ply, twisting to strands and again counter-twisting to rope introduces a fourth, unnecessary obliquity dynamic to affect strength. More becomes less.

If average premium quality tossa filament strength is calculated at an average 4.3MPa, twisting two yarns together decreases overall strength. 7.5lb being ~0.45mm and containing an average 40 filaments per yarn in cross-section. Therefore 15/2 yarn of identical material with a total average 80 filaments has a theoretic 341MPa. 15/1 yarn twisted from the same will be ~ø1.0mm, and contain an average 100 filaments in cross-section and 426MPa, ~25% stronger.

Additionally, count variation (CV) is measured by taking sections of yarns after spinning and weighing them to establish, effectively the diameter tolerance; the average number of filaments. A good ±2.5% CV will mean yarns could have 2.5% more filaments, or 2.5% less – the weakest point.

Most yarn mills will supply way outside this tolerance unless specified, quality inspected, and approved before export, when it can no longer be returned. Many mills will also not have enough drawing stages to manage the batched, piled and carded fibre to a stable slither ribbon width and bulk density entering the spinning machine. We are fortunate to have 4 drawing stages.

Yarns are twisted to match applications, eg. a carpet backing yarn needs to have wear abrasion, but longitudinal strength is not so critical. Yarn spinning twist settings for various CB yarns are matched to pass through carpet making machines at different given speeds by model, eg. CRT for Van de Wiele’s Carpet Rugs Tronic weaving looms.

As depicted in the graphic, there’s an optimum twist setting to attain maximum strength. Below this it will weaken due to incoherence – the filaments are too loosely twisted, and above, twisted too tight again weakens due to lateral stress transposing longitudinally into the yarn.

Visually, eg. 14lb is difficult to differentiate from 15lb yarn. The only way to estimate jute count in rope is by measuring the diameter of the rope, counting the number of yarns, and reverse calculating where it’ll still only be a reckoning.

Beware the sounds your rope may make under load. Especially after wet processing, you may hear crackling sounds. These are generated by elongation breaks in filaments, and while may sound ‘cute’, they’ll be deteriorating the overall strength of your rope. If you hear a ‘ripping’ noise and your rope lengthens with load, this is a very bad sign, generally caused by inferior fibre, or pre-processed material (eg. bleaching). For safety, these should not be used for suspensions.