Is this pillow firm or soft?

It is a down pillow, so it is soft and moldable rather than supportive. It suits sleepers who like to sink in and shape the pillow; side sleepers who need firm neck support should look at a down-alternative or a firmer fill.

What does RDS certification mean here?

The Responsible Down Standard certifies that the down comes from ducks or geese that were not force-fed or live-plucked, with traceability through the supply chain. It is a sourcing claim, not a measure of fill quality.

Does it fit a standard king pillowcase?

Yes. At 20 by 36 inches it is a standard king pillow size, so it fits most king pillowcases and shams.

How does it compare with a down-alternative pillow?

Down is lighter and molds more, but it needs fluffing and can trigger allergies. A microfiber or polyester alternative holds shape better and is washable, but feels less airy.

How should I care for it?

Down pillows generally need a pillow protector, regular shaking out, and occasional airing. Check the care label before washing; many down pillows are dry-clean or professional-laundry only.