Thanks for trying to help me out, guys.
You see, i don´t own the room. I just rent it. So i can´t re-model it too much. I think the company that own the house don´t mind in the end when it´s done and the room is isolated at my expence. If they even notice it.
I will keep renting for 6 more months or so. So when i move i don´t want to move out leaving a 1000 dollar project behind. I can pay maybe 100-200 usd.
I am going to just grow tomates, and different herbs like i did before these grows. When i am done with these plants and when my crossbreeding i plan on doing is done, it´s just a vegsteblegrow. At least for a while.
I even killed two of my Purple Mazar

seedlings yesterday, when i had an apiffanny. It´s getting too risky to grow here in my apartment becouse social services will soon start to visit us, me and my fiance. They are going to visit us becouse of sins in the past. Years ago. It´s just rediculous. But i don´t want to bore you guys with this. I went a little off topic there so back to the subject.
I am thinking that it should be enough to cut out pieces of glassfiber and fit them on the walls. Maybe 20 centimeters (8") thick. Then nail isolating-plasticsheet on the isolation. Then i will maybe have to use silicone or tape if there are any open spaces that need to be filled.
I was also thinking of skipping to isolate the concrete-floor. I will not cover the floor with anything, but i am going to isolate the walls all the way down to the floor ofcourse. I am thinking that this will maybe make it possible to grow in the summer too. The room is getting really hot in the summer. But with isolated walls, and ceiling. The heat stays outside.
I just want my growroom to keep the temp at a good level. The lights will heat up the place so i don´t think i will need to have a 100 proof isolation. And in the summer i have my plants outside.
This is a link to Wikipedia. A little info on Sweden. Just scroll down a bit to see a table on the tempratures in the different cities. I live in "Goth-town".

It is in the southern parts of the country. Right now the weather is really cold, and it´s snowing, but soon the spring is here, and it´s going to warm up.
http://en.wikipedia.org/wiki/Sweden
I want to thank in advance to anyone that helps me out, and give me feedback. I am going to post some pictures of the room so you can see for yourselves how it looks.
Have a good day. /H.