Peter Brown made a serviceable mallet from melted down plastic wood jugs.
HDPE is the plastic used in many household containers including gallon sized milk jugs. I melt down about 7 milk jugs and 3 powdered lemonade containers to get enough HDPE to make my mallet head.
The handle of the mallet is made from a cherry board and adds a nice warm contrast to the plastic! This mallet packs a punch and is quite heavy given it smaller size!