Lightweight silicone oil.
Silicones are intregral to high-end cosmetic formulating. They are used in all kinds of products: hair, skin, personal lubricants. Silicones can make the bulk of a formula (as in a hair "shine spray" or be a small addition to one (as in a lotion looking for improved spreadability).
Cyclopentasiloxane. This product is considered a "volatile fluid" in that it will disappear into thin air if you leave it uncovered (just like alcohol). Very lightweight!
Flash Point: relatively low flash point of 77C (169F), making it a semi-hazardous product to handle. Keep away from flames and sparks.