Plastisol is the plastic used for making soft baits such as senko worms or jig trailers.  On a technical basis it is a suspension of PVC particles in a liquid plasticizer.  It is unique because when it is made the two parts remain separate.  When the plastisol is heated the two components combine dissolve each other and the composition changes.  As the Plastisol then cools, it goes from a liquid state to a flexible plastic.  Aside from its use in making soft baits, it is also used for screen printing, particularly on outdoor products.  

To use plastisol you pour the liquid into a heat safe container.  I personally recommend using a Pyrex or other borosilicate glass container (a lab beaker or similar would work as well).  Borosilicate glass is used in labware and some measuring cups because it is less prone to cracking/breaking/exploding from rapid changes in heat.  Once you have poured the plastisol into your container it needs to be heated to 325-350 degrees.  The most common way to do this is with either a hot plate or a microwave. 

Each has its up and its downs.  The microwave works faster, but you have to keep a really good eye on it.  Taking it out, mixing it, & measuring the temps.  Sometime you need to add the plastisol back in for as little as 5 or 10 seconds at time as you approach the target temperature but in general, its fast and effective.  Personally I have used a hotplate for the majority of my plastic baits.  The benefit to a hotplate is that you can have a finer degree of control over the temperature.  You can even leave it on low to keep your plastisol warm while you mix in colors or unpack your molds.  The downside however, is that you must constantly stir the plastisol.  If you don’t, the plastisol at the bottom near the hotplate will get too hot, while the rest of the plastisol hasn’t warmed.  This causes the plastisol to take on a yellow tinge, or can even burn portions to a dark brown or black and have to be tossed out.  

One of the coolest features of plastisol is that after it is set, it can be warmed back up to its liquid state and repoured.  I keep a lot of my broken or damaged baits, especially senko worms.  As the worms start to get beat up and torn in the middle from being used on wacky rigs, I will pull them off the hook, rip them in half to recover my o-ring, and set them aside.  When its time for more worms, ill warm up a batch of plastic and toss the old worms in at the end.  They melt back down into the rest of the mix and can be used to make your own senko worms or other baits.  I also keep the scraps from the bottom of my pyrex container.  After each batch of plastics I take a zip top bag, label it with the recipe I used (ie. 5 drops green, 3 drops motor oil, 4oz salt in 2 cups of plastic), and then I put the scraps I peel out of the bottom of the purex in it.  Next time im making the same batch, I throw the scraps in and repeat.  Plastisol isn’t expensive, but I just like to recycle what I can.  It also helps me eyeball what recipes make what color, because I basically have sample swatches of each recipe. I label my finished bait bags in the same way, so that I can reproduce them.