User Review: Patagonia Puffball Sweater
Fabric: Ripstop Nylon
Price Paid: $55 on sale
Synthetic filled jackets of this type (also made by TNF, Marmot, Moonstone, Mountain Hardwear) could be considered as a replacement for either fleece or a down sweater, but really they fall in the middle and are best for specialized applications.
They may be warmer when wet than down sweaters, but they really aren't any lighter (for the same warmth) as down and are considerably more fragile.
As a replacement for fleece, they are lighter, more compressible, and more wind-resistant, but they are also far less durable and don't breathe nearly so well.
I use this over fleece and under a shell for really cold skiing and for knocking around town in the Montana winter. For this it's fine (adding more and more layers of fleece quickly becomes restrictive) but beware of certain limitations:
The shell is 1.3 ripstop and very susceptible to snagging and tears (especially around the seams)
The zipper is ridiculously small and easy to snag
The insulation batting tears (developing lumps and cold spots) very easily
Then again, it is mildly water repellent, dries quicker than fleece, and is warmer and lighter than the thickest pile (Patagoina retro-pile, Polartech 375 bi-polar).
You just have to be very careful with how you treat it.