When comparing the cost of polymers, can I just look at cost/lb of material?

No. Tests have shown that a minimum of 5% polymer solids to the weight of cement is required to eliminate the 7 day wet cure (the primary reason polymer is used). To ensure the mix design has 5% polymer solids, you must first know the solids content of the polymer to be used. For 100 lbs of cement, 5 lbs of polymer solids is required. Forton® VF-774 is 51% solids, so 10 lbs of VF-774 would be needed to get 5 lbs of solids or 5.1% polymer solids in the mix. A competitive product with 47% solids would require 10.6 lbs of polymer to achieve 5% solids in the mix. Algebra can be used to compare prices:

($1.96 / 0.51) = ($x / 0.47)
0.51x = (1.96 * 0.47)
0.51x = 0.9212
x = (0.9212 / 0.51)
x = $1.81

So if Forton® VF-774, at 51% solids, costs $1.96/lb, a competitive product at 47% solids would have to cost $1.81/lb to have a truly equal cost.

Disclaimer
This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.