Who doesn’t know this situation: you once again want to compare apples and pears. You will quickly realize that they are both fruits, but have some significant differences. This situation is similar to that of the chemical materials polyamide (PA) and polyethylene (PE). They are both part of mountain sports and sewn slings (sewn runners) are created from both.
We will explain the features each material has, what the significant differences are, and when it is better to take the pear instead of ending up biting a sour apple.
What types of runners are there?
Thick ones (nylon)
Wide sewn runners are typically made of polyamide, or to be more precise polyamide 6. These were first used in mountain sports in the beginning of the 1940s.
At the same time, in the USA, the first dynamic climbing ropes were being brought onto the market under the still common trade name nylon. To date, sewn runners and accessory ropes are made from the same material.
You can buy nylon slings by the meter, which are sewn as sewn slings or quickdraw slings. The number of lines in the middle indicate the strength. 1 line correspond to 5 kN.
Thin ones (Dyneema)
There are also new wafer-thin slings. Those are the ones you always load carefully and cautiously, because your mind tells you: “we were very brave today for trusting such a thin piece of equipment with our lives“. They are made from polyethylene and available for purchase in the mountain sport market since 1990. You can find them as slings under their trade name “Dyneema” or as accessory ropes.
The fibres of polyethylene are so smooth, that it is impossible to dye or tie them. Therefore you can recognise them easily by their shinny white colour, and they are always sewn and available for purchase as a sewn or quickdraw sling. Nowadays, many models have a colourful edge that is made of nylon. This makes it a mixed fibre but with polyethylene as a main material.
Polyamide versus Polyethylene. Or maybe both?
Nowadays there are sewn runners in all imaginable variations. Short slings, long slings, thick slings, thin slings, yellow, black, green and red. Before we move on, an important similarity – at the same time a reassuring feature – must be mentioned, which all sewed textiles made for mountain sports have: they meet the requirements of the European Norm (EN) 566, which regulated a minimum breaking force of at least 22 kN. This applies to quickdraws as well as sewn slings – no matter if made from Dyneema or Nylon.
In practice, this means you can feel reassured about packing both materials on your next climbing tour. You will find a suitable and certified selection here. And it makes perfect sense to take both. Why? We will explain:
The old friend Polyamide
Polyamide, compared to polyethylene, is heavier, has a lower tensile and cut resistance and soaks up moisture. This does at first not seem to be a recommendation for purchase. Nevertheless polyamide has features which can become of interest to you. Polyamide is more elastic than polyethylene and can therefore absorb more energy. Slings made from polyamide are cheaper than Dyneema slings and have the previous shown advantage: they are wider. This is an advantage because the polyamide slings used on ground level can guarantee safety whilst your brain is thinking of all imaginable life-sustaining measures at a dizzying height… a not to be underestimated fact on exposed multipitch routes.
+ It is more elastic and thus takes more energy
+ It is cheaper
+ It is wider and thus can be helpful for the mind
+ It is available in various colours which makes the logistics on the ground level easier
– It weighs a bit more
– Tensile and cut resistance are slightly lower
– Soaks up moisture
Your new best friend Polyethylene
In some situations, the “thickness” of the polyamide sling is a serious disadvantage. For example, when you are in an exposed position, standing trembling meters above the last anchor, facing the last seconds of your life because you discover that your last sling is way too wide to fiddle through the narrow crack. For these situations, the thin Dyneema slings are ideal. On top of that, slings made of polyethylene have, despite their low average mentioned above, a six or seven times higher edge stability than the equivalent made of polyamide (cf. Berg and Steigen 3/12). The edge stability (also cut resistance) is a very important aspect when making hourglass outcrops or head slings, which is why polyethylene is better suited in these situations than polyamide.
You can only buy polyethylene in sewn form as a knot would not hold because of the slippery surface. You also do not have to worry about the breaking load of your Dyneema sling being significantly reduced in the event of the knot “running” due to heat and the low melting value of polyethylene.
You should however keep an eye on the aging process of the thin polyethylene slings (6-8 mm). Due to their low weight and small diameter, they age faster and as such lose their breaking load sooner and faster than their wider counterparts or sewn runners made of other materials. Experiments have shown that after 3-5 years, the breaking load values decreased to 13-15kN (Bergundsteigen 3/2014). If a knot is added (which reduces the breaking load by 60%), then the breaking load value drops to a borderline area.
You can also use the slippery feature of Dyneema by properly knotting a sewn Dyneema sling and converting it into a shock absorber. This is however something for specialists and should be left to them. Take note: a knot halves the breaking load of a sling.
+ It has a high edge stability
+ It fits even into the smallest hourglass outcrops (if you want it to)
+ It absorbs less water, which becomes of interest for ice climbing
+ It is very lightweight
– It ages faster and has a decreased breaking load
– It is only available as a prefabricated round sling
– It has a lower melting point
Turning to the collective: sewn slings are also available as mixed fabrics which combine polyamide with polyethylene. They are, so to say, the all-rounders amongst the slings and are suitable for all discussed scopes, including advantages and disadvantages.
Their colour and strength makes them easily recognizable. They often contain a lot of white and are very thin, as is shown in the picture (manufacturer Mammut). The sewn runner is only 8mm wide but also webbed with a red band, which cannot be Dyneema.
Knots, wind and weather
Lastly, there are two things you should keep in mind: Knots can decrease the strength of slings to about 60%. This applies to both polyethylene as well polyamide.
Problematic for both materials, but in general for all textile products, are permanent installations and as such signs of wear due to weather (UV-radiation, moisture) but also excessive use (abrasion, number of falls), whereas polyamide is more stable than polyethylene. We therefore recommend that you use Fix-Exen, fixed hourglass outcrop slings etc. with great caution and examine them precisely before use. In case of doubt, “safety first” always applies. Your health and your climbing partner will be grateful.
In summary, one can say that polyamide and polyethylene, as well as apples and pears, all have a right to exist. In combination, they are not only flavourful valuable companions for your next tour, but if used properly will last for many years.