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Rigid Foam (Silpak)
USD 50.80
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Sculpture Depot
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Silpak SP-328-4 urethane foam consists of two parts (A and B) that, after mixing, form rigid foam products with a molded density of 5-8 lb/ft³. These rigid foams can be used for ca
sting parts or filling voids; consider SP-328-4 foam for production of decorative objects, lightweight mold shells, production parts, models, patterns, fixtures, duplicate masters and general tooling use. .sd-rf { --sd-brand: #5681cc; --sd-brand-deep: #3f66ad; --sd-brand-soft: #eef2fb; --sd-paper: #f6f7f9; --sd-surface: #ffffff; --sd-ink: #232831; --sd-muted: #5f6670; --sd-line: #e3e6ec; --sd-line-strong: #ccd1da; --sd-serif: "DM Serif Display", Georgia, serif; --sd-sans: "Libre Franklin", system-ui, -apple-system, sans-serif; --sd-mono: "JetBrains Mono", ui-monospace, monospace; box-sizing: border-box; width: 100%; max-width: 820px; margin: 2.5rem auto; font-family: var(--sd-sans); color: var(--sd-ink); line-height: 1.6; -webkit-font-smoothing: antialiased; text-rendering: optimizeLegibility; } .sd-rf *, .sd-rf *::before, .sd-rf *::after { box-sizing: border-box; } .sd-rf__eyebrow { font-family: var(--sd-mono); font-size: .72rem; font-weight: 500; letter-spacing: .18em; text-transform: uppercase; color: var(--sd-brand-deep); margin: 0 0 .6rem; } .sd-rf__title { font-family: var(--sd-serif); font-weight: 400; font-size: clamp(1.7rem, 4vw, 2.3rem); line-height: 1.1; letter-spacing: .005em; margin: 0 0 .55rem; } .sd-rf__lede { font-size: 1rem; color: var(--sd-muted); max-width: 62ch; margin: 0; } .sd-rf__block { margin-top: 2.6rem; } .sd-rf__block-head { display: flex; align-items: baseline; gap: .9rem; margin-bottom: 1.1rem; } .sd-rf__block-title { font-family: var(--sd-serif); font-weight: 400; font-size: 1.35rem; margin: 0; white-space: nowrap; } .sd-rf__rule { flex: 1; height: 1px; background: var(--sd-line-strong); } /* ---- Shared spec sheet ---- */ .sd-rf__specs { border-top: 2px solid var(--sd-brand); border-bottom: 1px solid var(--sd-line); } .sd-rf__spec { display: flex; align-items: baseline; gap: .65rem; padding: .72rem 0; border-bottom: 1px solid var(--sd-line); } .sd-rf__spec:last-child { border-bottom: 0; } .sd-rf__spec-k { font-size: .94rem; color: var(--sd-muted); flex-shrink: 0; } .sd-rf__spec-dots { flex: 1; border-bottom: 1px dotted var(--sd-line-strong); transform: translateY(-.28em); min-width: 1.5rem; } .sd-rf__spec-v { font-family: var(--sd-mono); font-size: .9rem; font-weight: 500; color: var(--sd-ink); text-align: right; flex-shrink: 0; } .sd-rf__spec-v--accent { color: var(--sd-brand-deep); } /* ---- Density grade cards ---- */ .sd-rf__grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; } .sd-rf__card { background: var(--sd-surface); border: 1px solid var(--sd-line); border-radius: 3px; padding: 1.1rem 1.2rem 1.2rem; } .sd-rf__card-head { display: flex; align-items: center; justify-content: space-between; gap: .6rem; margin-bottom: .55rem; } .sd-rf__card-name { font-family: var(--sd-serif); font-weight: 400; font-size: 1.12rem; margin: 0; } .sd-rf__chip { font-size: .68rem; font-weight: 500; letter-spacing: .04em; text-transform: uppercase; color: var(--sd-brand-deep); background: var(--sd-brand-soft); border-radius: 20px; padding: .15rem .55rem; white-space: nowrap; } .sd-rf__metric { display: flex; align-items: center; gap: .55rem; margin: .2rem 0 .85rem; } .sd-rf__metric-k { font-size: .76rem; color: var(--sd-muted); flex-shrink: 0; } .sd-rf__metric-track { flex: 1; height: 6px; background: var(--sd-line); border-radius: 3px; overflow: hidden; } .sd-rf__metric-fill { display: block; height: 100%; background: var(--sd-brand); border-radius: 3px; } .sd-rf__metric-val { font-family: var(--sd-mono); font-size: .73rem; font-weight: 500; color: var(--sd-brand-deep); white-space: nowrap; flex-shrink: 0; } .sd-rf__use { margin: 0; font-size: .85rem; color: var(--sd-muted); line-height: 1.5; } .sd-rf__note { margin: 1rem 0 0; font-size: .82rem; color: var(--sd-muted); font-style: italic; } /* ---- FAQ (static, always open) ---- */ .sd-rf__faq-item { border-bottom: 1px solid var(--sd-line); padding: 1.15rem 0; } .sd-rf__faq-item:first-child { border-top: 1px solid var(--sd-line); } .sd-rf__faq-q { font-family: var(--sd-sans); font-size: 1.02rem; font-weight: 600; color: var(--sd-ink); line-height: 1.4; margin: 0 0 .5rem; } .sd-rf__faq-a p { margin: 0; font-size: .97rem; color: var(--sd-muted); max-width: 66ch; } @media (max-width: 620px) { .sd-rf__grid { grid-template-columns: 1fr; } .sd-rf__spec { flex-wrap: wrap; } } Rigid Urethane Foam Light enough to lift, rigid enough to tool A two-part urethane foam that mixes and expands into rigid, workable parts - used for casting, filling voids, lightweight mold shells, models, patterns, duplicate masters, and general tooling. Specifications TypeRigid urethane foam ComponentsTwo-part (A + B) Density grades4 / 8 / 12 lb/ft³ Molded density (4 lb grade)5-8 lb/ft³ Best forTooling, models & fills Choose your density SP-328-4 Lightest Density4 lb/ft³ The most economical grade - well suited to void fills and lightweight cores. SP-328-8 Balanced Density8 lb/ft³ A middle grade that balances light weight against added strength. SP-328-12 Strongest Density12 lb/ft³ The densest and strongest - holds finer detail for durable masters and tooling. Higher density trades yield for strength and detail. Molded density for the 4 lb grade is 5-8 lb/ft³ - denser than free-rise because the foam is packed into a constrained mold. Sizes & pricing 4 lb kit$50.80 16 lb kit$121.20 80 lb kit$455.00 Pricing is the same across all three density grades. Availability varies by grade and size - check the size selector for current stock. Frequently asked What is Silpak SP-328 foam used for? It is a two-part rigid urethane foam for casting parts and filling voids, and for making lightweight mold shells, models, patterns, fixtures, duplicate masters, and general tooling. How do I mix it? SP-328 comes as two parts, A and B. You combine and mix them, and the blend then expands and cures into rigid foam. What densities does it come in? Three density grades: 4, 8, and 12 lb/ft³ (SP-328-4, SP-328-8, and SP-328-12). The 4 lb grade has a molded density of 5-8 lb/ft³. Which density should I choose? Lower-density foam (4 lb) is lighter and more economical, good for void-filling and lightweight cores. Higher-density foam (12 lb) is stronger and reproduces finer detail, better for durable masters and tooling. The 8 lb grade sits in between. What kit sizes are available? SP-328 is offered in three kit sizes: 4 lb, 16 lb, and 80 lb. Availability varies by density grade and kit size, so check the size selector for current stock. What does molded density mean? Molded density is the foam's density once it cures inside a constrained mold, which runs higher than its free-rise density because more material is packed into the cavity. For the 4 lb grade, that molded density is 5-8 lb/ft³.
