I like to think of this track like a short sprint - you've got six minutes to go from nothing to fully fleshed out idea before the music becomes too overpowering and knocks you off.
Sigur Rós are awesome and unless you speak Icelandic (or gobbledegook,) it's perfect essay writing music as you can't understand a word that Jónsi's singing.
But back to the sprint...
It's a classic steady increase in intensity - think Ravel's Bolero (actually we should totally add that to the playlist,) in that it has a steady beat running through it but the instrumentation builds and the song grows and grows and carries you along with it.
By the time you're hitting the four minute mark the track's getting pretty gnarly, the percussion steps it up, new instruments are being added, the volume certainly feels as though it's increasing and then finally, the guitars kick in at 4:35 and you're full on, hell bent for leather chasing the idea down before it falls of the cliff and disappears for ever.
Yeah, so, if you're trying to hammer out an idea, take this out for a spin.
Also, you should totally see the video - it's pretty gnarly too!