### Clue: Penguins are rarely so exhausting, as before (8)
### Answer: HARDBACK 
 ### Explanation: Definition: Penguins are rarely so
  (My last one in; I hope I've got this one right.)  HARD(exhausting,eg. a problem so hard it takes it out of you) + BACK(as before, in time or position, as in "back issues of a newspaper", or "put that book back"). 
Answer: The books published by Penguin Books are almost always paperback editions, and are rarely hardback/hard cover.