Why do some handheld target pads have a double-layer design? I remember using a single layer pad when I was a kid. Since then, the double layer design has been introduced.
At best I can tell, it makes a louder noise when you hit it, but that's it.
I have my own guesses, but I wanted to check with manufacturers first to see why they designed them that way. Sadly, after checking 7 different manufacturers at Amazon, I am convinced they are all the same manufacturer, because the product descriptions were suspiciously similar - and suspiciously inaccurate. Nevertheless, I did also check a name-brand manufacturer (Century Martial Arts; Everlast does not carry one), and they provided a better explanation.
They all say "This double sides target is ideal design for practicing high and low kicks, Enhance your speed, accuracy and strength", or "You can use this to enhance your speed, accuracy and strength", or similar. Century says the clap provides better audio feedback.
In my experience, single-ear target paddles don't last as long as double-ear targets. My reasoning is a guess, but I'd say that the design has to do with lessening the impact on the trainer holding the pad, and as well, reducing the damage to the pad. Here is my reasoning:
When you kick the target, your foot imparts a force onto the pad. The pad imparts an equal and opposite force upon the foot. In a single ear, there is less mass in the target, and so, the target takes more wear and tear. When the target contains more ears, then there is more mass, and the target can more easily absorb some of the force imparted upon it by the foot. This should reduce the force imparted upon the trainer, who will notice less fatigue in the wrist and arm as he holds the target. Also, the double ear targets seems to be replaced less often than single ears.
And why not one gynormous elephant ear target, rather than two smaller ones?
My guess has to do with more physics: when the first pad is kicked, it absorbs some of the kick, and allows its own momentum to be thrust into the second ear of the target.
For practical reasons, the double ear target does make a loud clap when struck appropriately; this, the manufacturers all say, can aid in developing kicks - the louder the noise, supposedly the better the kick.
To me, though, this is not the ideal training purpose; if the kick was sufficiently loud, it means a full kick was issued - and at some point that kick must be stopped, or else the kicker will develop knee problems. The heavier kicking pad will help reduce that, making for a safer kick. Air kicking (or kicking against a flimsy target) is fine for light kicks. But when kicking fast and hard, I would recommend the safe way and kick a kicking bag which will absorb the kick enough to save the knee (whether the kick is a round, front, push, or side kick).
Conversely, when a trainer wants to work in fast combinations, a lightweight target will more easily allow the trainer to position the target. Again, it's all physics. In this case, less mass means it can be positioned much more quickly.