I've been a Lair member for many years now, and have made four separate Pred suits, all on a small budget, for use in making fan films. We at the Lair are always happy to help with any Pred questions.
There are two basic ways that most people make their Pred dreadlocks. The first is to cast them in foam latex. That is pricey and takes some skill. The other way, which takes less skill and is cheaper, is to use "backer rod", also called "caulking tube", which is lengths of foam-rubber rope that are used to seal the cracks in walls before plastering or spackling over them. You can find backer rod online, or in most hardware depots. When I use it, I cut a long taper into each end; some people use hot water to melt them into a tapering end. Some people coat their backer rod dreads with Plastidip; some don't. Some people use the same size backer rod on all their dreads; some make the dreads at the sides of the mask thinner and shorter, and the ones at the back of the mask longer and fatter.
For the rings that slide up onto the dreadlocks (known as "dread beads") I have cast my own from resin, made them from PVC pipe or copper plumbing connectors, and cut them from a Halloween "skull/spine beer tube".
Photos of my Pred masks, to make all this clearer:
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Pred mask made from posterboard, with dreadlocks made from backer rod and cast-resin dread rings.
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Pred mask made from posterboard and foamie sheet, with dreadlocks made of thicker backer rod, and dread beads made from PVC pipe couplings decorated with three-dimensional fabric paint.
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Pred mask made from a modified pepakura coated with fiberglass resin, with dreadlocks made from thinner backer rod, and dread beads made from segments of a Halloween "skull/spine" beer funnel.
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Pred mask made from the plastic "blister pack" of a Halloween demon mask, with dreadlocks made from thin backer rod and cast-resin dread beads.
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Pred face mask made from a modified Rubies Halloween mask--I added dreadlocks made from backer rod and dread beads from cast resin, and also added inner teeth made from a Halloween "werewolf" set and mandible fangs cast in resin.
You can see three of my complete pred suits in action in one of my fan films, here (the 3 preds show up at the 6-minute mark):
Predators: The Hunt - YouTube
Hope that helps.