If a channel becomes better suited for a closed audience, it can be converted to private. Private channels are best for discussions that shouldn’t be open to everyone.

Bear in mind

• By default, owners, admins and channel managers can convert a channel to private, but owners can restrict this permission further by restricting private-channel creation. If you can’t convert a channel to private, find an owner and ask for help. 
• The #general channel can’t be converted to private.
• Channels with people outside your company will only be converted to private for the organisation that makes the change.
• Files shared in the channel won’t become private.

Note: On the Business+ and Enterprise Grid subscription, owners and admins can convert channels to private with channel management tools.

Convert a channel to private

When you convert a channel to private, a message will post in the channel to let members know that it’s been converted.

Note: Converting a channel to private is permanent, and you won’t be able to make it public again.