The felin resemble large bipedal cats for all intents and purposes. They tend to have fair faces, somewhere between animal and human in appearance. Their full-body fur coat comes in many colors and patterns, mostly earthen tones, golden browns, grays, and various pastels. Their head hair, distinct from their fur, may have the same colors, along with darker tones.
Felin eyes noticably glow yellow in the dark. This is not reflection, they glow with their own light. This and a sensitivity to a narrow band of infra-red allows the felin a fair degree of darkvision. They have no whiskers
Felin almost always have a feminine appearance no matter their biological sex or gender -- most of them simply appear like flat-chested females. So long as their groins are hidden, even other felin cannot tell if one is male or female. This plays a large role in felin sexuality, language, and dress, as bisexuality is the norm, there are no gendered pronouns, and no concept of gendered clothing.
Rarely, a female may show significant breast development. This is linked to a particular recessive gene. Even more rarely, a male may show beard growth. This is also caused by a recessive gene, and is distinct from having a shaggy chin. The rarest felin of all is the Blessed (felHu in Felinese), a true hermaphrodite who cannot express the breast or beard gene but does have both male and female genitalia.
Felin of both genders have the uncanny ability to completely nullify their fertility. This is an innate biological process thought to have evolved after their primitive ancestors overpopulated to the point of unsustainability. The Blessed are "stuck off". Either way, this has no effect on their usually impressive sex drive. It takes about a week to fully process the switch, and most felin go infertile most of their life.
The felin skeletal structure is light and springy, granting enough flexibility to curl up in a ball with some training. On the whole, they are hardier than their fair appearance might suggest and able to land from significant height with no lasting damage.