Damage To The Car You Borrowed
If someone else causes an accident and is 100 percent at fault, that at-fault driver would be responsible for any damages to the car you borrowed as usual. If you had full or partial fault or caused non-accident damage, the owner's insurance policy would usually apply.
Comprehensive and collision coverage follows the car, not the driver. Note that there may be some exceptions. Some people may choose to exclude all other drivers to lower their insurance premiums. Or you may not be covered if you have regular access to the car but aren't named on the insurance policy. (Think families or roommates for this condition.)
If the owner's comprehensive or collision coverage doesn't apply, your own car insurance might cover the claim similarly to how it might cover rental cars. See your policy for details.
Coverage For Liability
Liability coverage, which handles property damage and injuries to others, is more complicated. Many liability policies cover people who the owner allows to drive their car. Most liability policies also follow the driver when they're driving another car.
As with comprehensive and collision coverage, members of the same household not named on the policy may be excluded. Some car insurance policies will exclude driving certain types of vehicles or cars you have regular access to. The policyholder may also choose to exclude other drivers or other cars to lower their auto insurance rates.
So, what should you do? Whether you're borrowing someone else's car or lending your car to someone else, make sure your own insurance policy will cover anything that goes wrong. That way, you don't have to worry about the other person having enough insurance or not understanding their policy and telling you coverage will apply when it won't.
Your Own Medical Bills
Medical payments coverage will usually follow the driver when they borrow a car. However, the owner's coverage might kick in if the driver doesn't carry this coverage. Again, check your own policy to confirm coverage.