Poly 15-3 is a 1:1 mix, filled polyurethane liquid casting plastic that has a 15 minute working time and a 3-12 hour demold time. The filler in Poly 15-3 gives it a dense stone-like feel making it ideal for backfilling cold cast bronze parts. The filler also makes 15-3 a very economical, low-cost resin. The filler also reduces exotherm so shrinkage is minimal.