I am putting my 2cents here. Without people arguing about "tensor" I didn't know that "tensor" was just a trademark name. I always though it was a technology. So I think the OP was also confused as well. A new technology with some characteristics that old technology doesn't have...
I might as well put my own two or three cents in. OP Julian may like it ot not, but calling Mantra a Tensor is both scientifically and (in some way) legally wrong, since it is a
registered name/term as some already mentioned. So, "Tensor Bios" is actually not a trademarked term, "only" registered which is somewhat of a sub-level of a trademark. There are companys out there that have trademarked some of their products containing the term "Tensor"; companys that have nothing to do with table tennis whatsoever.
Anyway, to understand why a rubber by ESN is a Tensor and rubbers such as Tenergy, Rozena, Mantra and the Mizuno Q-series are
not Tensors, you probably have to go back in time a little bit...
As some of you know, ESN was founded by Dr. Nicklas, who studied chemical engeneering and has a PhD in physics and mechanical engeneering and who also happens to be the founder of the brand "Donic" (
Doctor
Nicklas). Also Dr. Nicklas played tt on a fairly high level (eventually 1. and 2. Bundesliga) and one of his coaches was Karl-Heinz Schreiner. Before establishing ESN, Dr. Nicklas sold Donic to his former coach and the Schreiner family still owns the Donic brand to this date. But thats just on a side note.
Back in the 90s, the tt companys had to solve a problem: producing rubbers to emulate the properties of (now "classical") rubbers that were usually speed glued, i. e. rubbers with a lot of catapult and outstanding spin capablities. At that time it was already discussed to ban speed glueing, which eventually happened about ten years later (after the Beijing Olympics).
Some of the stuff you can of course read up on the ESN homepage. ESN did a lot of research and was able to
integrate some sort of organic substance between the molecules of the rubber, i. e. topsheet and
which worked as a kind of a spring between it, and by doing so
also enabeling the topsheet to stretch beyong its normal capablities. And this technology is basically what ESN calls "Tensor" or "Tensor Bios". Stiga, for example, would have most likely been sued by ESN if they had marketed the Mantra or Airoc (which I believe are made by Daiki in Japan) as "The new Stiga Mantra/ Airoc, the best "Tensor" in the world!"
In 1998 the first Tensor was released, the Joola Tango, quickly followed by rubbers such as Andro Revolution, Revolution Fire, Tibhar Rapid Dtecs, Rookie Dtecs, Schildkröt v-max and s-max. However the Joola Tango was not the very first rubber with a high tensioned topsheet. One year earlier Butterfly released the Bryce. Butterfly therefore coined the term "High Tension". The effect might be simlilar to what ESN developed, but it was simply a different technological method. In essence both ESN and Butterfly developed at around the same time a topsheet which is
already under high tension before it is glued onto the sponge, but the topsheet of the Tensors gave the rubber an additional spring effect. The main problem with the first generation of Tensors was that the topsheet was very brittle, so the durablity was very poor and many of the very first Tensors had a bad reputation because of that. Some people were so bold and speed glued the sponge of the Tensors, although that was not necessary, further stretching the topsheet until bubbles appeared and essentially destroying the rubber and adding to the bad rep...
The main difference between the Bryce and the Tensors was/is, that a Tensor is desigend to
fully replace rubbers that had to be speed glued in order to be competetive (such as Sriver, Donic Coppa, Yasaka Mark V etc.), wheareas the Bryce still had to be speed glued to get out its full potential. It is save to say that ESN did something to the sponge of their first Tensors as well (they surely didn't start with factory boosting Bluefire, Evolution and so on...); but the real breakout was the way they produced the topsheet, hence the registration unter the term "Tensor". The sponge of the Bryce on the other hand was merely an upgrade of the already existing ones by Butterfly and still some lightyears away from the Spring Sponge of the Tenergys.
So, the
true revolution by Butterfly was the porous "Spring Sponge" that gives, along with the "High Tension" topsheet, the Tenergys their (probably still unique) speed glue effect. Sure, other factors play a role as well, such as the pimple structure. The pimples of the T64 are thinner compared to the ones of the T05 or T25 enabeling the ball to penetrate deeper into the sponge and get more catapult from the Spring Sponge.
At the end of the day, both ESN and Butterfly successfully developed rubbers with built-in-speed-glue-effect.
ESN's "revolution" was the "Tensor" topsheet (and later, after the success of the Tenergys, adding porous sponges, some of them factory boosted),
whereas Butterfly's actual revolution was the Spring Sponge while further modifying the High Tension topsheet.
As for the Stiga Mantras, Airocs, Mizuno Qs etc. which are made by either Daiki or Fuso, they are not quite as revolutionary. It might sound a bit harsh, but I have the impression that Daiki/ Fuso are oftentimes imitating or modifying interesting ideas by ESN and Butterfly. But they can produce very good rubbers as well; I like the Mantras and also the Mizuno Q3 and Q4.
Spring Sponge, Tensor, OCS, Cycloid, Hyper Elasto etc. are fancy ways to say
something, the difference is that some terms are either trademarked or registerd and some are not, sometimes for a reason. ESN probably knows better than us why they have registerd the name "Tensor" and what makes their rubbers different from the rubbers of their competitors.
Edit: Some additional reading for the ones interested...
https://www.tabletennisdaily.com/forum/showthread.php?5658-What-Is-a-table-tennis-tensor-rubber
http://ooakforum.com/viewtopic.php?f=44&t=3906&sid=7df25c62a365ef37d9f14c97f7800102