Firelog made of chemicals and compressed shavings. Doesn't throw off much heat.
The Firelog burns for two hours and increases the probability of successfully lighting a fire by a mediocre 7%. They are not very weight-efficient at only 60 min/kg however, despite what the description says, firelogs actually create more heat per hour of burn time than any fuel source in the game except for Coal.
Overall, they are really not that useful. If a long-lived fire is desired, cedar is the best choice and if a particularly hot fire is desired, sticks are the best choice. Both are renewable and more convenient to use.