These plastic rods are sounded by stroking with rosined fingers or high traction gloves to excite longitudinal vibrations in the rods. This pattern of vibration, with wave fronts reflecting back and forth lengthwise in the material, is similar to the patterns in wind instrument air columns, and people sometimes comment that the pliffers sound like a recorder. Waves travel faster in solid materials than in air, so the rods must be longer than the equivalent air column would be to produce the same note. Plastic was chosen as the material because harder materials such as metal would require even longer rods. (See, for instance, the instrument called Dansal 3.)
In the two photos on this page, two versions of Pliffers appear.
The audio for this page is a three part piece recorded by multitracking. Because the instrument is often uncooperative, I wasn’t able to record the parts in single takes, but instead had to do a lot of retakes and edits to make it come together.
A video of this instrument can be found among the demonstrations in this youtube playlist.