a solid material that is synthetic (= artificial, not found in nature), that has a very low density (= mass relative to its size), and that is made by replacing the liquid in a gel with a gas

When solidified, aerogels make good insulation for a spacecraft or aircraft. 凝固后，气凝胶可以为航天器或飞机提供良好的隔热效果。

Jackets lined with aerogel can keep you warm in temperatures of 50 below zero. 以气凝胶做内衬的夹克可以在零下50度的温度里保暖。