jwolthuis - 2:18 am on Jun 9, 2011 (gmt 0)
It sounds like "Aerosol with soap". Check the MSDS, Section 14, to be sure.
This is Class II Div 2.2, and is permitted to ship via First Class Package plus Delivery Confirmation, or Priority Mail with free Delivery Confirmation (now called Tracking Number).
Add an "ORM-D AIR" sticker, and "Shippers Declaration for Dangerous Goods", 3 copies, signed. Takes about a minute to fill-out the form.
If you can ship via First-Class Package, the Post Office is prohibited from inspecting the contents, by law (see DMM 188.8.131.52). This is your best option for shipments under 13 ounces.