I like a wide cut synthetic bag, with a thinner down or one of the many fleece liner bags .
Synthetic is Heavier, but cheaper and better performing in wet / humid conditions.

For backpacking in dry conditions down still has the best warmth / weight ratio.

PrimaLoft Gold has an interesting insulation “ boosted “ with CrossCore Aerogel.
Very lightweight aerospace material with amazing weight and insulating characteristics.
Don’t know how well it stands up to washing. Might be a hand wash proposition like down.

LlBean had a couple of PrimaLoft synthetic bags with this insulation. They seemed a tad pricy.
Patagonia has a lighter weight iliner bag with CrossCore.



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