Optiphen

Optiphen

INCI: Phenoxyethanol (and) Caprylyl Glycol
Usage rate: 0.5% – 1.5%

Optiphen is a broad-spectrum preservative you'll see quite often in natural products mostly because it gets the job done and it's paraben-free and formaldehyde-free.

There are a few types of Optiphen.  So when you're looking around to see which one to get, decide by the types of products you're most likely to make.  

I chose to use the regular Optiphen initially because the manufacturer said there were no pH restrictions.  However, according to lotioncrafter.com, they're now recommending to use Optiphen in products with a final pH of between 4.0 – 8.0.

Since it's oil-based, it's also used in anhydrous (products without water/aloe/etc) mixes like whipped butters.  It can also be used in creams, lotions, salves, and body scrubs.

It works well as a stand-alone preservative or you can use it in addition to other preservatives.  

Optiphen PLUS

INCI: Phenoxyethanol (and) Caprylyl Glycol (and) Sorbic Acid
Usage rate: 0.75% – 1.5%

Optiphen PLUS is another version which seems to have been created to function well in acidic formulas.  It is also paraben-free and formaldehyde-free and is a broad-spectrum preservative.

Optiphen PLUS is most effective in the products you're trying to make that will have a pH of 6 or below.  

So for example if you're going to be mostly making hair products which require a low pH to be most effective, Optiphen PLUS may be better to use.  However, be mindful that some emulsifiers (like the finicky Ecomulse) can become unstable if the pH you're trying to get is below 5.

Optiphen ND

INCI: Phenoxyethanol (and) Benzoic Acid (and) Dehydroacetic Acid
Usage rate: 0.2% – 1.2%

Optiphen ND is also paraben-free and formaldehyde-free.  It can be added to any phase of your formula, even before heating so long as you keep your temperature below 176 degrees Fahrenheit.

However, it is recommended to be sure the final mix of your product has a pH of 6 or below for it be effective.  

It is advised to also be careful because it contains benzoic acid, which can be "de-activated" by non-ionic emulsifiers (like Olivem 1000) and proteins. Yikes.

Related
http://www.theherbarie.com/Optiphen.html
http://www.ingredientstodiefor.com/item/Optiphen_PLUS/87?category=32
http://www.theherbarie.com/Optiphen-ND.html