CHECK MY LISTINGS FOR ALL SLEEVE TYPES (And larger quantities!): 
Right here!

These soft plastic sleeves are resealable and are made for storing DS and 3DS plastic game cases to protect them from shelf wear and other damage. They also work with the custom game boy color GBC / game boy advance GBA / game boy GB / Atari Lynx game case type that is purchasable from third parties. See photos for examples of these game case types.

Very good for collectors to keep their game cases in top condition.

You will receive 20 loose plastic sleeves. They still have the seal covered and are ready to be used.

THEY WILL NOT WORK WITH OFFICIAL GAMEBOY CARDBOARD GAME BOXES. ONLY OFFICIAL NINTENDO DS / 3DS CASES AND THE CUSTOM THIRD PARTY GAMEBOY GAME CASES.

EUROPEAN CLEAR DS CASES WILL NOT FIT INSIDE THESE SLEEVES SINCE THEY ARE LARGER. European 3DS cases will though.

These sleeves also are a great fit for north american NES cartridges (just the cartridge)

The current batch has the adhesive on the main portion instead of the flap. This makes it easier to remove the contents from the sleeve.

At this quantity to keep the shipping cost low I will fold over the sleeves inside the envelope to decrease the overall size. This is to keep the price low for you due to shipping size restrictions.
If you don't want them folded you can:
-purchase the 40x amount where they are always shipped flat.
-message me that you want them unfolded before purchasing anything so I can make you a listing with adjusted shipping price.