Balloons

Yesterday I went out walking, and decided to go to the grocery store. On my way, Bug and I saw someone release a bright yellow balloon with a big smiley face on it. Up, up, up it went! We stopped watching and watched the balloon race higher and higher into the sky. We watched it go until it was nothing but a small black dot. It made me wonder what happens to things when they go up so high. Does the balloon disintegrate into small particles and get blown about? Does it eventually lose its gas and come back down? Does anyone know?