The fill in that bag is probably the old 'Polarguard" polyester, a hollow filament fiber that TNF used instead of the more popular, lighter, (but not as durable) Qualofill polyester fiber. That was back in the day when their bags were 'over-engineered', so that if you bought a bag rated for 30F, you would be warm at 30F, and the bag would last. I had one of their bags, a 'Bigfoot' model, and it lasted quite a few years. The only reason its gone is a raccoon got into my tent and tore it up. I still have a down-filled 'superlight' model from that era that I bought for $99 at their discount store in San Leandro (just south of Oakland); at that time the regular price was about $170. Its just a hi-thread-count ripstop nylon fabric shell with 550-fill down, rated for 15F, and it still works great.