I use rubber since the chance of training injuries from the trainer blade are almost completely removed. Steel, aluminum, wood and, now, kydex, represent too much of a risk for injury, although they are far more realistic in handling.
Steel, aluminum, wood and, now, kydex, represent too much of a risk for injury,
Especially when cold.
I've heard that Kydex can become brittle when cold, but I've not been able to replicate the results of your experiment.
Be carefull! Getting stuck in the eye with a plastic knife can blind you just about as easily as a real one.
...with eye protection...
Anyone that trains with knives that doesn't wear protective eyewear is foolish.