Glass, also known as Ice, is light blue in colour. Among the three kinds of blocks, this one can be easily broken by all kind of birds. Levels with these blocks are often provided with The Blues , as they are very good at breaking these blocks. It is suggested to multiply. the bird in front on the glass block to maintain the greatest strength of the bird. Most birds slow down when they hit glass, but Chuck slows down after only breaking one bit of glass.
The Blues are very helpful on destroying glass, especially when "shotgunning" or better, when split.
Strangely, Chuck is weak against glass, despite glass having a much weaker strength than wood & stone.