Shipping to Puerto Rico (US)
Even though Puerto Rico is part of the United States, if you ship there from the continental United States, you will more than likely be charged like it is going to be an International shipment. This is mainly because of it being an island and the distance, but also for the Customs process and handling that it will still have to go through once it arrives.
Customs in Puerto Rico (US)
Because of some security issues in the past, the Customs department in Puerto Rico has really stepped up their game in the past several years. They have always held the right to search your shipment as it enters the country to make sure it complies with their laws and the correct paperwork has been filed, but now they are more likely to do so as opposed to that right just being on paper, so to speak. This translates into a longer Customs process as a general rule of thumb. You can help your shipment to move through Customs without much hold up if you try and have all the appropriate paperwork filled out and attached for them to examine once it gets there. Any missing paperwork will cause your shipment to see delays.
Security concerns when shipping to Puerto Rico (US)
There is some security concerns when shipping to Puerto Rico because there has been, in the past, some drug related shipments that have moved in and out of their ports as well as their airports. Because of this type of criminal activity, the vessels are now much more closely monitored and the Customs process is a bit more rigorously that it had been in the past. Generally speaking though, your parcels tend to make it through the Customs process and to their intended recipients without too much muss of fuss.