The concept is called "Fan Tossing". Use a worn in, flat, humid deck. Do a thumb fan, but instead of placing your left thumb(assuming your making the fan in your left hand) so close to the short edge of the deck, move it in half an inch to an inch towards the center of the deck. This will make the fan a little bit smaller. Before you start tossing them in the air, squish the cards together quickly by pushing your middle finger and thumb together, through the fan. Then toss away, but make sure your thumb isn't stuck to the top card of the fan.
Fan tossing is a great summer concept because it takes advantage of the humidity in the air(If it is humid where you are) by making the cards a little bit sticky. It can also help if your hands are sweaty, but this will cause your thumb to stick to the top card,or bottom depending on what moves you do.
When catching the fan make sure to keep your four fingers together. Then absorb the fan by bringing your arm down as you catch it, or spin it if you are catching a spinning fan. Just slap that thumb on top and have fun with it.
If you want to practice with creativity in this concept, make a fan, then glue, or staple it together. Now you have a fan that wont fall apart, and you can throw around to see what looks cool, and expand the possibilities. Have fun!
-Lang
http://www.LangFlourishing.com