ISA Cyclic Loading Tests on Weblocks


The ISA had recently the opportunity to test Slackline material using completely different methods with access to new testing machinery. Trending usage like Trick-Highlining has led to important new questions regarding gear fatigue, which needed to be answered by testing. In a first attempt, the ISA testing-team started to test cyclic forces and gear resistance on 4 different slackline weblocks.

How to test Cyclic Loading and what it may represent

We see more and more slackliners finding spots to set up their “perma-rigg”, especially for regular bounce and trick-training. Those situations are a great example of typical cyclic loading forces for a weblock (a continuous on-off pulling force from bounce, leash-fall and specific tricks).

We all know, loads and forces on slack and highlines depend on many different factors like length, material, tension and age, as well as the weight of a slackliner. In order to simulate scenarios closest to real life situations, a minimum, maximum and average standard of loads had to be chosen. From the few data conducted until today, the ISA testing-team chose three different load ranges in order to represent forces closest to maximum in “real slackline-life” scenarios. (Please find the more precise explanation of the choice of forces for these tests on the ISA website directly: TESTS



The ISA test results, based on their developed force and load standard, have shown us some not life threatening, but definitely caution demanding results for the SLACKIBLOCS with a serial number including “XXXX2017” & “20XX2018”.

It is therefore in our biggest interest to share a better understanding of the tests done, the results found and the consequences and care we would like to share with the slackline community and specifically with our customers who own those older SLACKIBLOCS. Generally we find ourselves only slightly disagreeing with the “real slackline-life” forces chosen by the ISA for these cyclic loading tests. After close conversations with the ISA about these tests, we understand the approach and the idea to choose loading forces rather a bit higher than too low, but therefore also our common decision to not see a product recall as a necessary consequence.

What’s different with the SLACKIBLOC from 2017 & 2018?

The results have shown a weakness in our SLACKIBLOC from the 2017 and 2018 batch, compared to the 4 other weblocks (one steel) in the test. The production process of those weblocks batches had been a cold bending mechanism, used in order to create its final shape. This is an outdated process for our weblock production and has been retired as a shaping choice.
All our following SLACKIBLOC weblocks* have been heat treated after and before bending for more resistant (cyclic loading tests on those are currently happening).

What we ask and recommend to SLACKIBLOC users from this series

In order to avoid any situation where a generated safety factor may become under special circumstances unreliable, we want to use those results and demand caution officially from all our SLACKIBLOC users, bought before the 1/4/2020.

Please read below which immediate action we recommend if:

  • You are using your weblock mostly for Trick-Highlining
  • It has definitely been used until today more than ca. 200 days in Trick-Higlinine sessions
  • It has been used on rather short and tight highlines (polyester around 30-40m)
  • You are trying trick-highlining and bouncing and maybe still falling a lot on a Highline with a body weight of more than 75kg
  • You are using it for perma-riggs (non-stop rigged and under tension)
  • You are using it often for beginner lines (short and tight) on festivals with high amount of leash-falls


  • ALWAYS make a weblock back up as indicated in our manual
  • Avoid short line (30-40m) trick-highlining on polyester webbing with those weblocks
  • Avoid using it in perma-riggs, short and tight beginner lines
  • If you don’t know about the past of your SLACKIBLOC (2017+2018), you feel like it’s rather old and a back-up solution is not enough? We offer you to send it to us for testing.
  • Your weblock has been really highly used?
    Please send us an email with the subject “TIRED SLACKIBLOC” at [email protected]. A return may be possible for further testing purposes and a replacement shall be sent to you (a SLACKIBLOC* from more recent, differently treated batches).

*The new SLACKIBLOC SH and SR version are heat-treated before and after bending, in order to delete any risk of internal cracks and strains - Cyclic testing has been organised for testing in March 2021 The new SLACKIBLOC SR isn’t bent at all, the metal plates are left straight and no bending is needed for the production process.


How do I know if my SLACKIBLOC is from this older series?
Simply check on the side of your weblock the serial number. Affected SLACKIBLOCS show a code which includes the number 2017 or 2018. If you bought your SLACKIBLOC after the 1/4/2020, your weblock is NOT AFFECTED.

I use my SLACKIBLOC for longlining. Do I need to be worried about using it?
No, the stated amplitude of strain gap combined with significant frequency cannot really be reached in longlining. In momentarily forces yes, but not as an average force that could break the longline - this is rather unlikely. WE ABSOLUTELY recommend either way, to create a weblock back-up - especially if you are a longliner of +75kg.

Why are there only the results from 4 different weblocks in the ISA test?
At the moment of the ISA’s testing opportunity, the group of testers had only access to a limited amount of weblocks. Also each test of one weblock demands an enormous time investment, which made it hard for them to compare more than 4 at the time the testing machines were available. Further tests and comparison are already planned by the ISA testing team.


We wanna thank the ISA testing team for the conducted tests and efforts in order to continuously help make our sport an even safer one. Also a great thank you to the community for understanding our call for action, our statement and proposition as a small slackline gear producer. We had simply never access, neither as a company nor through our manufacturers to have conducted these kinds of tests earlier. We are more than happy to see the attention of the ISA team regarding new slackline trends that change the usage of gear and needs to adapt therefore our perspective to safety and production processes.

Thank you !



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