There is a lot in the score, 70 piece orchestra and 16 piece female choir. I spend a lot of time with granular synthesis plug-ins modifying both the orchestra and other sound sources to create the held tense sounds that run through the more claustrophobic cave scenes. Thematically the key bit for me was a scene with Sarah and Beth, if you're seen the film you can work out which bit, otherwise I can't spoil it.

Insomnia was a much bigger project, for this I used a fifty-six piece orchestra, but still kept a lots of electronic effects as the atmospheric backgrounds. For the electronic side I should say that I like using synthesised sounds, I don't see them as second best to orchestral. The electronics half of it couldn't be scored, it's drone, effects, loops. Then to add an orchestra on top of this gives in my opinion the best of both worlds.

Thematically most of the music comes from two pieces, the opening sequence were Dormer and his partner fly into Nightmute, 'The Glacier' on the CD, gives material for Walter's theme and the theme that is Ellie's relationship with Dormer. Then there's a theme that serves for Dormer and Kay's theme.
Spoiler (but I assume you must have seen Insomnia if you're reading this). This was always know as the 'Death Music' in the temp. We first hear it in the background on piano as Will looks round Kay's bedroom, returning for the death of Hap and finally in it's biggest orchestration at the end when Will Dormer dies.