I happened to find a good price for a Natu, and ordered one in size 1, though I already have more than enough cups. In some pictures, the Natu looked different from the Si-bell, in others the same.
Anyhow, for all those who always wondered, the Natu size 1 is almost identical to the small Si-bell. The only difference is that the walls are a bit thinner, the Natu cup therefore softer than the Si-bell.
In the below picture, you can clearly see more through the Natu (left) than the Si-bell (right).
Everything else is the same. Not sure how I could get the softness charts updated to reflect this, any ideas?
Update: I just realized that what I have is the OLD natu, the new one has the natu logo across one side and is a bit rounder in shape. Bummer - they sent me old stock.