'The Wisest Son'

Once an old called his three sons. He gave them equal money and ask them to buy something that can fill their living room entirely. He told them that he will give all his money and property to the son who is able to do this task as asked.
The first son buys sticks and tries to fill the room but he falls short of sticks. The second son buys straw but he also falls short of filling the room. The third son buys only two things and he is able to fill the room completely and thus earns all the property and money.

What did he buy?

Test to find the wisest son

Here is what did he buy! 

Source 

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