how is insulation measured and what does it mean?
 

how is insulation measure compared to its warmth? i know its in grams per square inch i believe but how warm is 40g insulation vs 60 or 80. and im guessing the more insulation at least in polyester the poofer the clothing?

also what are the different types of insulation and how do they compare?

meter not inch.
150 is for arctic and 40 is for 0°C. This is for Thinsulate.

Where are you going where you'll need an insulated jacket?

+1
I have a Jacket w/o ANY insulation. I had no problem even with -28°C. Just had dressed on a thin fleece long-sleeve under jacket. But, to be honest, I wear ass and back protectors all the time, and they make some warm too, especially on a chair lift.

not a jacket, pants. i have 40g pants and im figureing on getting a 15mm shell instead

I ride in the mid-atlantic and an insulated jacket was the best investment I've made for snowboarding. I have a Stoic jacket with like 20/15k waterproofing/breathability and 100g synthetic insulation. The waterproofing might be over-kill, but I don't think I'll buy another jacket without insulation. I used to ride with just a shell and a fleece, but this is so much better. All I need is a t-shirt or long sleeve shirt for anything down to like 15*F.