Whenever an item is vulnerable to moisture or liquid, it is important to consider how the item can be protected from moisture or how the liquid can be insulated form getting other items wet. The approach for protecting vulnerable items can depend on the threat. For example, when packing items that are vulnerable to large threats of moisture, such as protecting books from rain or accidentally spilled water, it makes more sense to protect the books themselves rather than try to contain the water that might damage them. On the other hand, when packing a specific container of liquid in a suitcase, for example, it is more efficient to contain the container of liquid when trying to protect the entire contents of the suitcase.
When protecting against moisture, the best material for protection is plastic. There are endless options for containing items in plastic when trying to protect them and the best option will depend on the size, shape and flexibility of the items. Plastic resealable bags are excellent choices for small items, both because they are inexpensive and are flexible enough to accommodate differently shaped items. For larger items, resealable plastic bags in extra large sizes are newly available. Plastic trash bags or plastic shopping bags are also inexpensive materials for protecting something from moisture. In cases where a large area needs a moisture barrier, such as a crawl space under a home, plastic tarps can offer large area coverage.
While plastic can provide a non-porous material for excluding water and moisture, making the packaging air-tight is the responsibility of the person packing the items. There will definitely be exposed seams if the packaging isn't made continuous by closing or wrapping, so it's important to tightly seal the items being contained or protected. It is also crucial, when containing the items in a wrapper that can get air in it, to exclude the extra air to avoid creating a "bubble" that can pop and leave the package vulnerable. If the items to be contained or protected are very valuable, it may help to "double-bag" the item within two separately sealed resealable bags. If the moisture hazard is more like damp towels instead of pourable liquids, extra plastic shopping bags can provide a water-proof barrier while also accommodating larger items -- besides being free and abundant in most situations where people have saved them. In situations where plastic is unavailable, any material that can help to keep moisture away from the vulnerable items even temporarily can be helpful. If plastic isn't available, wrapping liquid containers in an absorbent material, such as a terry towel, will help to absorb any liquid that escapes and help to prevent vast quantities of liquid from escaping and rolling around in the container. In the case of shipping a liquid, packaging the liquid containers with an absorbent material, such as shredded newspaper or cardboard, can be an extra precaution in case the liquid breaches the plastic wrapping.
When mailing liquids via the United States Post Office, USPS, or United Parcel Service, UPS, the outer envelope must be labeled to indicate the nature of the contents. Containers of liquids must be closed with screw-on caps, soldering or clips to contain the liquid. The outer envelope must be strong enough to protect the contents.
When flying with liquids, new security regulations put severe limits on the amount of liquid that a passenger can travel with in their carry on. Passengers can travel with up to 3.4 ounces of a liquid. The Transportation Security Administration recommends putting liquids in checked luggage. However, there aren't specific rules about traveling with other items that are damp. but aren't specifically "liquid," such as baby wipes and damp towels. To protect them and other dry contents during travel, it can be helpful to quarantine them in plastic as discussed above.
