What follows is most of my reply to a question about glycerin to the yahoo soapbubble fancier's group, 8/16/2005

My take on Glycerin & Walmarts, now that you've brought it up: In experimenting with various kinds of glycerin I was interested in their viscosities (thicknesses) as well as it's ability to attract water/moisture from the air (hygroscopic trait). Viscosity would help to counter gravity's pull (top to bottom) of the liquid in the bubble skins thus making it suffer from old man disease = "thinning at the top". Glycerin’s hygroscopic abilities would be helpful as there are times of the year here in New England where humidity is extremely low.

Most off the shelf glycerin’s I found were in the skin care isles of drug store chains, as you suggest. At Walmart though, I found what I've come to call the "good stuff"—behind the counter of the pharmacy available only by request.

The skin care isle glyc. is more viscous, usually comes in a brown plastic bottle and is labeled with a warning not to eat it. The Walmart Glycerine comes in a brownish glass bottle (4 oz. for $4.08) is less viscous and easier to integrate into bubble brews. The Walmart glyc. was about a third more expensive but it performed it's hygroscopic duties better than the other, though it was less viscous... which lead me to discover personal lubes & more on that later.

When I called the company that bottles the "good stuff", they explained it was a more refined, all vegetable derived (mostly coconut and some palm), kosher grade, glycerine "USP" which is often used in delivery of medicines (you could eat it). Further research into kosher grade vegetable glycerin and I discovered it's also used as a sugar substitute in many "health food" recipes and for folks trying to control their blood sugar. So I tried a health food store. There I found the "good stuff" at less than half the price I was paying for either the skin-care isle, or Walmart bottles. As you've discovered it's also sometimes used in premium soap making and aroma therapy products.

I was intrigued too that my favorite glycerin is mainly derived from coconuts as is Sodium Lauryl Sulphate, the surfactant which makes most everything in your house bubble, including most dish soaps. My non-scientific reasoning went like this, "perhaps the common coconut base for the glycerin and surfactant were more complimentary than the less pure ingredients found in less expensive glycerin."

Anyway, you may find it cheaper to shop around at health food stores and see what they have to offer. There you'll find vegetable/kosher grade and not the less refined, thicker "who knows what's in it because it's often a byproduct of the soap making process in which they sometimes render animals for their fat content". Note: only one of five health food stores in my area had the "deal" I was looking for. The others had glycerin but it was wicked expensive.

I started investigating viscosity boosting ingredients that would promote a more supple bubble skin with greater self-healing properties for my big outdoor bubbles so they would shatter into smaller bubbles rather than just pop when the wind tore them apart. Long story short, personal lubes offered what I needed.

I buy Kosher Vegetable Glycerin OSP Aroma Therapy Grade 100% pure, by the gallon from The Essential Oil Company, Portland Oregon. You can find them on the web (along with many other companies) or their phone number is 1-800-729-5912.