Silnylon, silpoly, or DCF (Dyneema) for an ultralight tarp?

Across specialist communities, silnylon is cheapest and durable but stretches when wet and sags overnight. Silpoly doesn't stretch and resists UV better. DCF (Dyneema Composite Fabric) is the lightest and doesn't stretch or absorb water, but costs several times more and is less abrasion-resistant. Pick based on whether weight, budget, or storm performance matters most.