Japanese beds and futons explained

Why are some futon much heavier?

The heavier ones are made of 100% cotton, a tradition that has almost died out

How did American futons develop?/ Why are American futons so different from Japanese ones?

Americans took the idea back after the post-war occupation, then hippies that took them up put them on pallets, probably to keep air circulating under them and so keep warmer and save the need to air them all the time.

Why do Japanese pillows have hard pellets in them?

 How did futons become popular in the West?