Any spearfishing supplier should have Dyneema, check with any retailer you normally go through. Normally is comes with a nylon sheething over it. Straight Dyneema with no covering is slick and you will have trouble with knots pulling out and it will also pull through a constrictor knot.
I need to find whipping twine to see if it works better for tying the constrictor knots.
I need to find whipping twine to see if it works better for tying the constrictor knots.