In Engpsh, "浓密的软毛" would be referred to as "dense soft fur". This type of fur typically comes from animals with thick, fluffy coats, such as some species of rabbits, cats, and dogs. Here are some example sentences using this phrase:
The rabbit's dense soft fur kept it warm in the cold winter weather.
The cat's dense soft fur made it look pke a small, cuddly ball of fluff.
The dog's dense soft fur was so thick that it was difficult to see its skin underneath.