By 
Since the Switch’s release earlier this month, many users have reported connectivity issues with the console’s Joy-Con controllers, with the left one in particular being especially noticeable. Many owners experiencing such issues have been sending in their affected controllers into Nintendo to get fixed.
To find out exactly how Nintendo has been solving these issues, CNET Australia recently sent in a faulty left controller. Once getting it back from Nintendo, they discovered the only thing that was changed with the controller was the addition of a small square of black foam, which you can see in the lower right corner of the second image below.
CNET speculated that this piece of foam is actually “a piece of conductive foam, which is foam that’s been specially treated with nickel, copper or both so it can shield electronics from RF interference.” They then went on to note that the foam is sitting directly on top of the Joy-Con’s antenna traces, too, which suggests that it’s protecting the antenna from interference.” To test this theory, CNET removed the bit of foam, only to find that the connectivity problems returned immediately, which proves that the fix was successful.
CNET then purchased another Switch from Amazon to test its controllers’ performance and found that this second console had no connectivity issues with the Joy-Con, despite having a lack of foam in the interior. Though there is no way to be sure, this could indicate that Nintendo is already on top of the issue and is already sending out improved controllers.
