Multi-walled carbon nanotubes in vertical "stacking" configuration. This model consists of 3 seperate tubes with varying diameter and height, tallest tube is around 20cm tall and 50mm wide. There are also two spacers included that center the tubes when the model is placed horizontally. This model is not accurate or realistic in terms of size and ratios and was just made with arbitrary values. This was designed in SOLIDWORKS, while it's not the best program for this (it takes 7 minutes to build the tallest model) it worked well enough for this.