The yellowish color suggests its kevlar.
There was a period some years ago when people were using kevlar as parachute rigging line rather than spectra or dacron due to its superior dimensional stability, but it has largely fallen out of use main parachutes and is only found in some reserves these days.
The kevlar that was being used on main parachutes (often packed on the ground and several times a day, rather than in a clean loft like reserves that are packed only every few months that are exposed to sun only if deployed) proved to be more vulnerable to abrasion and the deteriorating effects of constant sunlight exposure than Spectra or Dacron line.
My experience with using this stuff as stooge release line mirrors that of the parachute industry. It will degrade and fray over time and constant exposure to the sun. OTOH, I have some stainless line sets that are over 30 years old that show no degradation at all.