A total of 7 Bears had at their sack for about 2 hours and were unable to breach it.
This is what Ursack posted:
April 18, 2014
We are still awaiting the official certification letter and number from the IGBC, but can share some of the details. At IGBC insistence, we baited an Ursack S29 AllWhite, knotted it securely and placed it on the ground with no aluminum liner and not tied to a tree. The first two grizzlies went at it for an active 57 minutes. One of the bears was nick-named "The Destroyer," but neither he nor his sister were able to compromise the Ursack. The Grizzly Wolf and Discovery Center rotates bears in and out at approximately one hour intervals. So the Destroyer went back to his quarters and five, count 'em, five more grizzlies came out to work on the same Ursack. The IGBC testing protocol requires a total of 60 minutes of active bear encounters, so even though we needed just a few minutes more to pass the test, there was no way to get the Ursack out until the five bears finished their shift. Not to worry. Ursack made if for another hour. A total of seven grizzly bears and two hours of active clawing, biting and scratching--yet Ursack survived. After washing the Ursack one could barely (bearly?) tell that it had been attacked.