Questions & Answers about Кошачья шерсть очень мягкая.
Why does кошачья end in -ья instead of a standard feminine adjective ending like -ая or -яя?
The word кошачий (cat's) belongs to a special group of possessive adjectives, mostly used for animals. Instead of standard adjective endings, they use a soft sign plus a vowel for the feminine (-ья), neuter (-ье), and plural (-ьи) forms. Since it modifies a feminine noun here, it takes the -ья ending.
Since шерсть ends in a soft sign (-ь), how do we know it requires the feminine form кошачья?
How would кошачья шерсть decline if I wanted to say I am allergic to cat's fur?
To say you have an allergy to something (аллергия на...), you need the accusative case. The inanimate feminine noun шерсть doesn't change in the accusative. However, the possessive adjective changes to its feminine accusative form, which ends in -ью. The phrase becomes на кошачью шерсть.
Why use шерсть for a cat's fur instead of мех?