New ultralightweight sleeping bag from PHD

Interesting. I'm not familiar with the 'Filler Bag' concept. Wouldn't the down probably get crushed crammed inside a normal bag? I guess you could use it paired with a quilt to minimize. But at 8.5 ounces, couldn't you just get a significantly warmer bag for another 5 or 6 ounces instead of yet another piece of kit?

Seems like this product would fill a very small niche in the marketplace. But there definitely are viable applications. Too bad I never go anywhere where a 59 degree bag would be adequate.

"Wouldn't the down probably get crushed crammed inside a normal bag?"

If the outer bag is big enough then it won't reduce loft of inner bag too much.

If you have two bags, then you have a second inner and outer fabric layer. This can weigh as much as the down without adding significant weight, so weight of total system could be 33% heavier.

It's just a lightweight liner bag.

Can do the same thing with a "multi-purpose" down puffy and depending on conditions, insulated bottoms. Montbell has had a similar bag liner for years.

That thing is being marketed towards "newbees"

If you need jacket and bottoms for comfort before going to bed then they add no weight, as compared to an inner bag.