Many Thanks to All!

@ Paul Davies

The weight before segmeting was about 2 kilos less.

@ Nick R.

I think the weight is OK because of the 2 kilos more from the segmenting process.
The dent factor is ok. Yesterday I was on the lake, I hit some rocks with the bottoms, I have some scratches but no indentation.

@ Robert W

I have made the long strips of polystyrene cutting the pieces of 1,2 metric at 45 degrees and joint them with hot glue.
It is not possible to paint because of the use of regular old acrylic spackling compound to fill voids between strips.
There was an old topic about building with polystyrene.

http://www.kayakforum.com/cgi-bin/Building/archive.pl/bid/11/md/read/id/53023/sbj/polystyrene-as-boatbuilding-foam/

This topic was the final argument to proceed with this project.

@ Mike Hanks
Yes, I read the topic. It would have been nice to see some picture.
I knew I was not the fist to use polystyrene in building a kayak, but I think I am the first in my country (Romania). And the combination of polystyrene and the segmenting the kayak may be a first in the entire world. But this was an "accident". I was not intented to do anything new.