Powder Snow

Powder snow is a trap block obtained from cauldrons.

Obtaining
A cauldron in a snowy biome will fill up with powder snow when it is snowing. Powder snow can then be picked up from this cauldron with a bucket.

Breaking
Powder snow does not drop anything when mined, even with Silk Touch, and tools do not speed up mining.

Powder snow can be picked up with a bucket.

Usage
Entities fall through powder snow without taking fall damage and move much slower in it, similar to cobwebs. Despite being a full block, it does not cause suffocation damage. A player whose head is within the block sees a frosty vignette decorated with snowflakes.

Powder snow can be used to make technical farms, instead of water.

Mobs or players wearing leather boots do not fall through powder snow. In this case the snow behaves as scaffolding when the player sneaks or crouches while on the block and jumps while inside of the block.

Freezing
When an entity is inside a powder snow block, they will begin to freeze, taking damage.

Wearing leather armor slows down the rate at which damage is taken. A full set of leather armor will prevent all freezing damage.

Trivia

 * "Snowier Snow" was announced to be part of the Mountains biome in the biome vote at MINECON Live 2019. One interpretation of Vu Bui's statement in Minecraft Live 2020 implied it to be a separate feature from Powder Snow. However, when "Snowier Snow" was first mentioned in the 2019 biome vote video, a block is seen functioning similarly to Powder Snow. Powder Snow is often referred to as "Snowier Snow" by the community, and it's possible that Powder Snow is one of multiple parts of the promised "Snowier Snow" feature, with the other part possibly being a parity feature such as Snowlogging, or some other as-yet unknown feature.