X the Unknown is terrific fun and a well-made genre entry that is obviously showing its age nowadays but, when put into context of the time it originally came out, stands head and shoulders above other notable films that are probably better known.

X-The Unknown shares with the Quatermass movies a belief in science rather than the motives of government…a creation of the Hammer horror studio before they discovered blood, gore, girls and other blandishments to offer the audience…

After a series of prolonged climaxes, with its potential victims staring directly into the camera and shaking with fright, the "Unknown" finally emerges as a type of rolling rubber mattress, disappointingly unhorrific in content and appearance.

Despite its absurd storyline, it's a surprisingly entertaining film that won't deaden your brain cells even if it's a trashy B film sci-fier.