This is what Nova Craft say on their website:
TuffStuff is a cutting edge composite made of basalt and Innegra fibers. Basalt fibre is made of melted basalt rock and Innegra is a fibre consisting mostly of polypropylene. When they are woven together into a cloth and infused with our high impact vinylester resin system, the result is simply amazing! TuffStuff canoes are a great choice for paddlers looking for a light canoe for extended flatwater tripping with more than enough strength to handle lots of abuse in the back country
TuffStuff Expedition is as the name suggests the perfect option for an expedition canoe Nova Craft's Incredible Tuff Stuff material made even stronger. A great option for wilderness trips and occasional white water use, stiffer for even better on the water performance in all areas. Only a few kg heavier than TuffStuff but still weighing in well under SP3.
This is how light TuffStuff is: