Pfft. Don’t waste money on that Grangers/Nikwax stuff; it’s just non-detergent soap*. I bought some pure soap flakes in Tescos for a quid something, does just as good a job, and enough for several washes. I also use it for my Gore Paclite jacket.
As MSP says; couple of tennis balls in the drier after. I take mine to the local launderette, where they have massive driers with more space. Takes a few quid to get it properly dry, but my Rab jacket is just about as warm as when I bought it 15 years ago!
*I think detergents break down biological material, such as feathers, which destroys the effectiveness of the down. Or something. Not good, anyway.