Does it come with a cap, so that once it’s opened and there’s some left or you have to stop spraying, it helps to keep it from drying?

Hello JoeG, Great Stuff™ cans with the Original Dispenser are considered one-time use and will seal shut if left to sit for more than 2 hours after its last use. Inserting a pipe cleaner sprayed with an oil lubricant into the dispenser MAY prolong the life of the product but restart is not guaranteed.    Great Stuff™ cans featuring the Smart Dispenser™ may be reused up to 30 days when used as directed. The Smart Dispenser™ should remain attached to the canister. Shake the can for a minimum of 60 seconds and remove any cured foam from the tip prior to dispensing. If foam is cured and does not dispense, do not force material from the cannister.    Neither the Original Dispenser nor the Smart Dispenser™ should be removed from the can when stored. Doing so will cure the foam inside the valve, making the can inoperable.  Check for the Best By Date on the bottom of the can as product may not dispense after date displayed.