insulation questions

[ponkass]

Hi...
I have some q´s about insulation.

I´ve been reading this forum for a couple of months and i´ve seen everybody talking about 2.5-3 pcf insulation is the way to go when isolating your studio

Is density the only factor that matters when choosing insulation type?
What is the "lamda" (don´t know if that´s the right name for it in english, it´s the same sign as in wavelength) figures in specs??
I figure it has something to do with heat??

Because in Sweden most insulationproducts don´t come with densityfigures but only with the "lamda" figures (37 for example)

Thankful for any kind of help... sorry about my english...

Andy