# Cushion Sponge Cell Architecture: Open-Cell Polyurethane vs. Rubycell Liquid Retention and Migration
TL;DR — The cushion's sponge is the compact's liquid warehouse: an open-cell network that holds the formula in its pores, meters it to the applicator under pressure, and stays in place inside the sealed system. The compact family records 16 catalog models with pan capacities from 1.7 ml to 20 ml, including a multi-pan layout of nine 0.9 ml pans. No sponge material is recorded in the material register; cushion sponge selection is a project-level decision, and the retention and migration behavior below is engineering guidance to be confirmed per project.
Why: The Sponge Is the Product, Not the Packaging
In a cushion compact the sponge sits between the formula and the user, so its cell structure decides the experience more than any other part:
- Retention is the warehouse job. The sponge must take up and hold the formula, dose after dose, without drying out, pooling, or starving the applicator;
- Release is the metering job. The network must give up the formula on pressure but not bleed it under gravity, in a bag, or on the vanity;
- Migration is the boundary job. Liquid that wicks to the pan rim becomes a leak path that the seal was never designed to stop;
- The program documents the format, not the sponge. Catalog models and pan capacities are recorded; the sponge itself is a project decision.
How: Cell Architecture as Storage, Metering, and Containment
3.1 What the compact family actually documents
The compact family records 16 catalog models, with pan capacities measured from 1.7 ml to 20 ml, including a multi-pan layout of nine 0.9 ml pans. The base substrate of each compact is a project-level configuration. "Cushion" here is a descriptive framing for a cushion-style sealed pan format — the same framing used for the sealed-pan compacts already documented — and the product record does not separate cushion into its own subclass.
3.2 Sponge selection: a project decision, not a catalog fact
No sponge material is recorded in the material register. Open-cell polyurethane and Rubycell are candidate material concepts — names common in cushion conversation — not catalog records. Following the same discipline as elastomer selection elsewhere in the program, cushion sponge material, density, and thickness are chosen and confirmed against project specifications, with no material sheet claimed.
3.3 Open-cell structure: retention and release as one balance
The behavior that matters is the connectivity of the pores. An open-cell network is a lattice of interconnected voids: the liquid is held by capillary forces across the struts and released when the applicator puff compresses the cell walls — press for a pickup, release for the next dose.
The engineering balance is that retention and release pull in opposite directions: a denser, finer network holds liquid more evenly and releases it more slowly; a coarser network meters faster but can drip or starve. Cell density, pore size, and the fluidity of the formula must be matched as one system. No retention or release rates are published — these are per-project measurements against project-defined targets.
3.4 Rubycell as a candidate concept, not an endorsement
Rubycell-style materials are a candidate material concept here: a name for a polyurethane-family sponge that appears in cushion conversation. That is all it is in this article — a candidate name. No Rubycell-style material carries any program-level approval, and no claims about a specific product are made on its behalf.
3.5 Migration and the sealed system
Migration is what happens when the sponge's liquid stops cooperating with the seal: formula wicks along the sponge network to the pan rim, toward the gasket seam, or down between pan and housing. That is exactly why the sponge cannot be validated on its own — leakage and vacuum testing (documented capabilities, no parameters published) stress the compact as an assembled system, while drop testing covers the portability that a fully loaded cushion meets in a bag.
<pre class="language-mermaid"><code>flowchart LR
A[Compact cushion format<br/>16 catalog models, pans 1.7–20 ml] –> B[Sponge selection<br/>per project, no recorded material]
B –> C[Open-cell structure<br/>retention vs migration, guidance]
C –> D[Sealed system<br/>pan + gasket chain]
D –> E{Leakage + vacuum + drop verification}
E –> F[Release per project]
</code></pre>
What: Verified Program Data and the Verification Hooks
- Product family: the compact family records 16 catalog models;
- Pan capacities: measured from 1.7 ml to 20 ml, including a multi-pan layout of nine 0.9 ml pans;
- Format framing: "cushion" is a descriptive framing for cushion-style sealed pan formats; the product record does not separate cushion into its own subclass;
- Component boundary: no sponge material is recorded in the material register; open-cell polyurethane and Rubycell are candidate material concepts, and sponge selection is a project-level decision;
- Verification hooks (capability-level): leakage test, vacuum test, and drop test are documented testing capabilities, with no parameters published.
Gotchas
- No sponge material is recorded. Do not quote a "standard cushion sponge": open-cell polyurethane and Rubycell are candidate names, and every property of the chosen sponge — material, density, pore size, thickness — is a project decision to be confirmed and documented at project level.
- Candidate names are not endorsements. A Rubycell-style material has no program-level approval; treat any mention as a candidate concept and never turn it into a product claim.
- Retention and release numbers cannot be borrowed. Doses per pickup, retention efficiency, and migration rates are per-project measurements; nothing of the kind is published by the program.
- The sponge is part of the sealed system, not an add-on. A sponge that wicks formula toward the rim defeats the gasket; validate sponge behavior together with leakage, vacuum, and drop tests rather than as an isolated material check.
- "Cushion" is a descriptive framing, not a catalog subclass. It describes a sealed pan format; the product record does not separate cushion into its own category.
Related Resources
- Category: Compacts
- Related insight: Airtight Cushion Compacts: Gasket Creep & Pan Sealing · Compact Godet Pan Retention · Compact Mirror Silvering & Corrosion · Cushion Compact Hinge 1000-Cycle Degradation · The 12-Test Lab Matrix
- Quality & Testing Capabilities — leakage, vacuum, and drop testing