According to the manufacturer (Maratac), the straps are a "composite" material. They have a embossed pattern (top, bottom, sides and ends) which gives the appearance of kevlar or ballistic nylon (which they are not).
The straps are water proof and have one fixed loop and one floating loop near the buckle. These are 20mm wide and do not taper, so the stainless steel buckle is also a 20mm wide item.
Some pre-order customers will be getting Ka La watches with the black case. So if I put these straps on their watches, then a black buckle would be needed. So I have ordered a black 20mm buckle of similar style from another source. When it arrives, I will put it on one of these straps and make another post showing how it looks.
(click the photo to see the strap in detail)I like the look of the strap with this Ka La model. It gives the watch more of a sporty feel. I will wear a prototype with this strap for a few days and see how the comfort compares to a leather strap.