It's a brand name for expanded polystyrene, the white stuff used for mainly for consumer electronics packaging. The term is actually a brand of BASF IIRC and used in german-speaking countries for this material, wether it is actually that brand or not.

Translation of first page
1)I'll start with a basic plan of the castle, and then belly-first on the rock-socket (off-2cm-styrodur were..
2)I interpret the rock structure at first only. I cut out this strip from the rough surface
3)Later comes the fine work that is suggested here already.
4)one side of the base rock I cut out, because I want there later times a "crypt".
5)stairs that lead down to the crypt, I carve all "lazy" of one block of 2 cm styrodur
6)then come the building creates a wall of each tooth and here's a "step-by-step"
7)I draw my first front wall segment on plywood. here I use a cardboard template for the outlines of windows or structures.
8)I say from the wall stuck. Cut out the outline of the window, I just say from the edge of - the carve you do not see more later.
9)Now I draw the same outline again to 6mm insulation. The wood is used as a template for Wanted location and shape
10)Then, the stuck-SELITRON is cut with a scalpel knife. the of the window (and generally in circular shapes) is the best with slow, "meaningless" movements. with the straight lines on the other hand, you can simply drag the scalpel flat.
11)Now come the bricks. with ruler and pencil, I draw my lines orientation initially 12)then I enter the individual stones with moderately pressure into the surface. Darfur itself is a rather dull, soft pencil or a pen.
13)The result looks something like this. best moves to the lines between the stones still twittering after times, to deepen the relief.
14)Behind the of the window opening, I still liked a grid and stained glass windows (optional). I cut the mesh with the skalpess from cardboard, which in turn is the template helpful.
15)Opening the window on the wood wall I glues a piece of mosquito nets, and consider writing my of the window cross from cardboard.
16)Now I can glue the wood to the wall.
17)then it looks like this.
18)and in the end I stick that one section of wall just to its position in the whole.
19)Round shapes are tricky. you can make SELITRON 6mm half round, by putting it with beden present "knead" and simultaneously turn the "knead" the compacted structure and prevents breaking of the material.
20)here the ready-bent SELITRON struck one sees squeeze on the back of the thumbprint from the
21)The front side is already smooth on the other hand remained
22)now recut the window and engrave the masonry.
23)here of course because I can not stick to wood behind it, I'm instead a smooth wall made ??of strong cardboard.
24)the stuck-together wall stucco has been bent back a bit now. so I fix it to dry with Scotch Tape on an appropriate role.
25)hint: SELITRON glued on very well with wood glue if the surface to be bonded with fine sandpaper roughen somewhat.
26)hint: SELITRON glued on very well with wood glue if the surface to be bonded with fine sandpaper roughen up somewhat. Now's first one dries stundchen ...
27)It pays to have the wall profile in the bent state nachzuvertiefen again.
28)how it looks after drying out.
29)Now comes the semi-circular space at its soller. missing the pinnacle.
30)the battlements arise again out of a stuck-6mm SELITRON 2, 5cm high.
31)I also carve the stones next.
32)This part is also bent into shape and is made between the fingers "kneaded" lest it breaks through.
33)Only when it is finished bending, I cut them from the battlements breaking will not be as easy
34)then comes the parapet on the soller
35)the gate wall gets a multi-layer constructs' a la gidian ": several layers SELITRON - and then working diameter
36)is now already times a little primed rankommen because I plug in later to some not so good will, meanwhile, is also the third floor of the glued floor (plywood)
37)at the 3rd I will have floor truss and therefore go a little differently. I prophesied paste styrodurstucken with wooden wall (wall) and Balks 38)the sequence: first glue the styrodur, then enter stones, then cut the gaps for pure timber truss
39)rounded truss beams I fooling with 3mm SELITRON.
40)here it is also a semi-circular stuck, this time from just above the other three semi-circle-bonded styrodur.
41)spire of curved cardboard.
42)grows so slowly third story.
43)to make such order for winding structures Roof, you do not need math.
44)I always just cut a rough cardboard template and then snip long turn around until it fits.
45)sufficient for straight roofs do I transfer the outline to be bent plywood with cardboard.
46)here is: what does not fit will make it fit.
47)extent until now. more later.
48)the roof of the castle includes several bay windows, chimneys and roof tiles of course
49)not to have to cut brick individually, "tooth" I strip of cardboard with the scissors. you can speed up things when using multiple stripes above the other sets and teething time.
50)In this brick castle should act fairly uniform. so I cut some teeth a little short.
51)of course it's a boring work I'm doing something in person (be honest) before the tv. Here is the inventory-to a 3 - hour film
52)then the overlapping strips glued to the roof
53)for circular roof you can simply pluck the cardboard in the form
54)in this way is also in such a roof around relatively quickly
55)Another bay window, chimneys and added turmchen