When determining the type of emulsion to use for your screen prints. There are a couple questions that can help narrow down the answer. What type of ink is the first question. Photo polymer emulsion is only for plastisol ink, and if you try using water based ink with photo polymer then your emulsion is going to break down quickly and the your stencil will be ruined. Another question to ask- what type of exposure unit do you have? Photo polymer emulsion is very fast exposing and the window for error is very small. So if you are using a homemade DIY exposure unit- you should try using a dual cure emulsion for your screens. Dual cure emulsions are easier to expose because the window for exposure time is much wider then photo polymer.
Here are a couple more tips to picking the right emulsion for screen printing.
Emulsion. There are three basic types of emulsion, and each have different needs for exposure. The 3 types of emulsion are photopolymer, diazo and dual cure. Dual Cure emulsion are the easiest emulsion for new screen printers to use. The "window" of exposure is the most forgiving of all three types of emulsions. Photopolymer is the fastest exposing emulsion- but the window is also the smallest, meaning the margin for error is very small for this type of emulsion. Diazo emulsion is the last option- which usually has a window of exposure comparable to that of dual cure.
Photopolymer; Plastisol Ink Only
Dual Cure Emulsion; Water Based Ink, Plastisol Ink, Discharge Ink
Diazo Emulsion; Water Based Ink, Plastisol Ink, Discharge Ink and Solvent Ink for sticker printing