The Thinkpad (I only own couple of very old old ones) has a semi-plastic case, but has quite a few special features to ruggedise it: (Quoting from https://secu

The Thinkpad (I only own couple of very old old ones) has a semi-plastic case, but has quite a few special features to ruggedise it: (Quoting from https://secure.wikimedia.org/wikipedia/en/wiki/ThinkPad#Lenovo_purchase https://secure.wikimedia.org/wikipedia/en/wiki/ThinkPad#Leno...) The following are some of the changes that have been made to the ThinkPad line: Added Magnesium-alloy chassis roll cage to reduce motherboard flex caused by holding the laptop one handed on a corner. Added Magnesium-alloy lid roll cage for a sturdier lid while replacing the lid material from magnesium-alloy to plastic for better wireless signal reception.[12] Added Carbon Fiber Reinforced Plastic to 15 in (380 mm) ThinkPad Models.*