The Kreuzspitze binding leashes are made with a kevlar core to be as strong and light as possible. Tipping the scales at a scant 16 grams (0.6 ounces), the leashes will scarely be noticeable on your feet. That is, until you yard-sale and don't lose your skis (phew). The leashes are made of kevlar, which is coated in polyurethane to protect from fraying. The attachment point at the boot is an aluminum carabiner-style clip which can quickly thread into a buckle strap or something similar. The end that attaches to the binding comes equipped with a polyproylene cord that will break under force somewhere around 80kg, which may help in an avalanche. The leashes are 24cm long when retracted but stretch to 48cm in order to reach higher buckles or attachment points.
Update 2019/20: Kreuzspitze added the option to connect directly to your ski instead of your binding. The Ski Attach kit includes a metal ring that screws onto your ski plus an extra carabiner, for quick unclipping from both your boots and skis (in lieu of girth hitching to your binding). This is great for bindings that don't have a good place to attach a leash, or you prefer to not interfere with your binding.