They can either be wood or aluminum. I encourage you to use a wood one. If not, I will make fun of you like I do my good friend Bill Booker at LaSalle-Peru H.S. for using his aluminum one. If you choose the wood fungo, I would recommend taping the barrel.  If you hit a good number of fungoes, the tape will increase the durability of the bat. I took the tape off of one once. The barrell was like sawdust, but I re-taped it and it was ready to go.  One season, I figured it out, between the  high school, American Legion, an junior high seasons I had hit over 10,000 fungoes. Tape it up!
As I had previously mentioned, the amount of teaching points is limitless.  The length of the game will really depend on how often you stop the action in order to discuss points related to base running, backing up throws, fielding techniques, and etc.  If you have assistant coaches, have them distributed throughout the field in order to help with certain teaching points on the spot, thus eliminating full stoppages of the game.  Now get out there and start putting the “FUN” back into fungo. I know that’s pretty corny, but I couldn’t help myself 🙂
One of the major advantages of wood fungo has to do with the feel of your hands. While the metal ones feature a conventional metal bat knob, their wood counterparts usually come in 2 knob designs. The conventional metal-bat style knob is excellent for folks whose hands are sweaty. The flared knob is amazing for those that do not want the knob beating their hand’s bottom which is uncomfortable during practice.
A fungo bat is a specially designed bat used by baseball and softball coaches for practice. The etymology of the word fungo ( /ˈfʌŋɡoʊ/) is uncertain, but the Oxford English Dictionary suggests it is derived from the Scots fung: to pitch, toss, or fling.[26] A fungo is longer and lighter than a regulation bat, with a smaller diameter. The bat is designed to hit balls tossed up in the air by the batter, not pitched balls.[27] Typical fungo bats are 35 to 37 inches (89 to 94 cm) long and weigh 17 to 22 ounces (480 to 620 g). Coaches hit many balls during fielding practice, and the weight and length allow the coach to hit balls repeatedly with high accuracy. The small diameter also allows coaches to easily hit pop-ups to catchers and infielders along with ground balls due to better control of the barrel of the bat.

For starters, we should clarify just what we’re talking about when we say fungo bat. Longer, lighter and thinner than a regulation bat (but a larger barrel), a fungo bat is typically 35 to 37 inches long, and weighs between 17 and 22 ounces. As David Allison wrote in the June 1978 edition of Country Journal, “A fungo bat looks to be a cross between a baseball bat and a broomstick.”