Mammillaria plumosa, the feather cactus, is a species of flowering plant in the family Cactaceae, native to Northeastern Mexico.

The clustering spherical stems, 7 cm (3 in) in diameter, are completely covered in white downy spines.

The spines are adorned with very long hairs that are arranged like the segments of a bird's feather and protect the plant against the blistering sun of the desert.

White or greenish yellow flowers are borne in late summer.

It has gained the Royal Horticultural Society's Award of Garden Merit.