Technically according to Celotex's Rep that spoke at our college material science classes about the product a number of years ago, they claim that with the proper nailing(staple) pattern it is considered structural when using thier sturdy brace product and does meet minimum ASTM standards for rack resistant wallboard. Because the company had donated many lifts of the product to our labs at the time for use and testing, I will never forget the backlash that the students gave him when he made these claims. We hated the stuff. He is correct though in thier certifications.Cellotex is a brand name for asphalt impregnated fiberboard sheathing. The faces are black (asphalt) and the interior is brown. It is quite soft. It is non-structural. Used as sheathing, every 5th sheet and all corners had to be plywood to provide minimum racking resistance.
I think one of the biggest headaches with fiberboard sheathing is that it tends to warp and bow, especially if it gets wet. The exterior walls end up being wavy.
There is a different but similar product used on roofs. Generally it is a light gray or white (not asphalt impregnated), and is higher density than the fiberboard sheathing. The stuff used on roofs is used for insulation, building crickets, and cant strips.
It is a sugar cane base product. The interesting thing about Celotex is that during the Katrina aftermath when we were paying 15 bucks for a sheet of 7/16" OSB it was still 6 to 7 bucks. People who normally wouldnt use it, started to just because of cost. These past few years as OSB supplyy capacity has caught up with demand and has dropped as low as 4.75 a sheet Celotex remained at 6-7 bucks. THis led to a huge drop off in demand and eventual sale and losure of several of the new plants that they had just opened. They were bought out by another company called Blue Ridge.
Just stick to OSB sheathing...