lizzie said:
Okay that was a stupid question, but what rigid material?
Fiberglass insulation, in the US it comes in 0.6m x 1.2m sheets in various thicknesses, 5 cm being perhaps the most useful. I don't know what's available where you are, but check with local building supply houses. The simplest approach is to build it into a picture frame--you could even mount a tapestry in front if you are clever!
You are looking for something like this:
http://www.certainteed.com/CertainT...ommercial/OEM+Acoustical+Board+Insulation.htm
Back to your original question, the recording part is easy, since you can close-mike vocals and guitars. That removes the room as a factor in the recording.
The difficult part is mixdown, since you need to be able to hear your mix in a relatively neutral environment. That's what using the panels will help you achieve.
Regarding your room, I'd get curtains in front of the sliding glass door too. Turn the bed the other direction, so the foot is next to the radiator (of course don't block the radiator). You need to move the speakers to your desk position, that's where you should mixdown. Try to center your desk on that wall, which is tricky because of the closet door. If you can make any improvements, replace that door with a bifold, which will allow you to get the desk more centered. Open the closet door when listening to your mixes.
I'd probably record sitting in front of the (turned) bed, with the mics facing away from the desk, and a bit into the headboard.