Can you insure cash through UPS or the US postal service ?

I want to know if I send $300 cash through mail if I can insure it ? A friend and I are having an arguement about this.

Can you insure cash through UPS or the US postal service ?
No, you can not. You can't even insure a money order. I know cause I sent my step-son a money order from USPS and it says you can not insure it.
Reply:USPS says to bring the cash (plus what you would have spent for the insurance) to the post office, use it to buy a postal money order, and then send the postal money order instead of the cash. This makes sense. I do not know UPS's policy.
Reply:Bad idea. Buy a money order.

perfect teeth