When we published the differences between the iPhone 6s and the iPhone 6s Plus, there were many including the weight between them. The iPhone 6s weighs 14g, more than the iPhone 6s Plus (20g more ), initially, this difference is due to the fact that the new Apple model 7000 series aluminum has been used, but there just is not so, if not the material used in the new models are lighter, and that there is more material than the previous model as confirmed Unbox Therapy.
Then, why they weigh more new models? If we look at the next picture, we can only think of one answer: the 3D Touch. The iPhone screen 6s / 6s Plus is the same as the previous model, with the only difference (although it is said that the glass is more resistant) that have a sheet over it will differentiate three types of pressure.
The (display) screen of the iPhone weighs 12 grams. iPhone 6s screen and weighs 29 grams. For 5.5-inch models, the iPhone screen 6 Plus weighs 19gr. iPhone 6s Plus screen and weighs 40g . The overall weight gain in both iPhone devices are 11% over the previous model, which is not much weight but it seems when you consider that this difference is mainly on the screen.
Despite the 11% increase over the previous model, we can not say that the weight has increased a lot when you consider that both devices are higher, wider and thicker than the previous model. Yes, it is convincing that some of that weight have offset the reduction of 5% of the battery, so most users would have preferred that the iPhone 6s / iPhone 6s Plus since it is heavier.