Hashing algo in Sia blockchain

Does anyone know what the hash function that Sia blockchain uses to hash the previous block header? My understanding is that Blake2d is used as a PoW function, but a different function might be used for hashing. Bitcoin uses SHA-256 for both, but zcash for example uses Equihash for PoW, but SHA-256 for hashing.

Sia uses BLAKE2b everywhere – for PoW, Merkle trees, transactions IDs, etc.