Instructables user gezortenplotz writes:

Wind across a microphone causes distortion and unwanted noise for videographers and nature recorders while taping outside. The purpose of the microphone ‘blimp’ is to attenuate the wind noise without interfering with the desired sound. Blimps are expensive. This project came in under $40. Mics are interchangeable in this blimp (if the mic’s diameter will fit inside).