A liquid is any substance that flows readily and assumes the form of the container, but retains an independent volume. For the purposes of mailability, a liquid may be a cream or paste or any other nonhazardous substance (except a gas) that may liquefy under existing conditions.
A powder is a substance composed of finely dispersed solid particles.
- Liquids and powders that are nonhazardous (i.e., not regulated as hazardous materials) are mailable provided they are properly packaged as specified in 451.3 and DMM 601.12.9.1 and DMM 601.12.9.2.
- Any matter that is a source of an obnoxious odor is nonmailable as stated in DMM 601.12.8.
Liquids and powders that are corrosive, explosive, flammable, toxic, or otherwise hazardous are subject to the mailing conditions for hazardous materials in chapter 3 and DMM 601.10, as applicable.
The following applies when mailing cremated remains (ashes):
- Domestic: Permitted for cremated human or animal remains only when sent via Priority Mail Express or Registered Mail service (DMM 503.2). The identity of the contents should be marked “cremated remains” (Label 139 preferred) on the address side of the mailpiece. The item must be packaged as required in 451.3b.
- International: When permitted by country, cremated remains may only be sent via Priority Mail Express International or Registered Mail service. Cremated remains and the class of service must be available to the destination country. The contents must be indicated on the applicable customs declaration form. Label 139, Cremated Remains, may optionally be applied to the address side of the mailpiece. The item must be packaged as required in 451.3b.
The following conditions apply:
- Liquids. Nonhazardous liquids, creams, and pastes (particularly those in 1–gallon paint cans with only friction–top closures) are often a source of damage to other mail and postal equipment. The proper packaging of liquids is critical to ensuring the integrity of the mailpiece during handling.
All liquids are subject to the general packaging requirements in DMM 601.1–8 and the following:
- Containers having friction–top closures are not acceptable by themselves. Such containers must be packed within a strong and securely sealed outer packaging.
- Screw caps with a minimum of one and one–half turns, soldering clips, or other effective means must be used to ensure a secure closure.
- Glass and other breakable containers more than 4 fluid ounces and any containers over 32 fluid ounces must be cushioned within a sealed, waterproof container such as a can or a plastic bag, and must be packed within a strong and securely sealed outer packaging.
- Steel pails and drums with carrying handles and positive closures (e.g., locking rings or recessed spouts under screw–cap closures) may be accepted without additional packaging.
- Powders. Dry materials that could cause damage, discomfort, destruction, or soiling upon escape (leakage) must be packed in siftproof containers or other containers that are sealed in durable siftproof outer containers.