# SAN (AS) vs. PETG in Heavy-Wall Packaging: Chemical Crazing, Transparency, and Mold Shrinkage
TL;DR — When a heavy-wall, transparent part needs a resin, AS (SAN) and PETG are the two names that come up, and the choice is really three engineering questions wearing one hat: chemical stability against the formula (crazing risk), optical appearance to the eye, and dimensional behavior in the mold. The material system's records anchor the conversation — AS (SAN) and PETG are both registered, AS-type usage is decreasing per customer-driven demand, PCR variants of both exist with project-level recycled content, and the cream jar family records PP+PETG constructions across 25 catalog models — but the chemistry numbers themselves (shrinkage, stress-crack thresholds, haze values) are not program data. They are configured per project, when the actual formula, the actual wall stack, and the actual mold meet.
Why: Three Questions Decide Between AS and PETG
When a buyer asks "AS or PETG?", the honest answer is that the resin name decides nothing by itself. The part's formula, its wall geometry, and its mold decide — and those three inputs map to three engineering axes:
- Chemical stability against the formula. The formula sits against the inner wall for weeks or months; crazing risk is a material-chemistry phenomenon and a per-project compatibility conversation;
- Optical appearance to the eye. Transparency is not a single material property — it is the result of material, wall thickness, mold surface, and processing interacting, and it is accepted visually per project;
- Dimensional behavior in the mold. Shrinkage differences between resins change what the cavity must be machined to; the answer lives with the mold and the injection molding capability of our manufacturing system;
- The records anchor, they do not decide. What the program can state cleanly: both resins are registered, the cream jar family is built on PP+PETG, and AS-type usage trends downward per customer demand;
- The numbers stay per project. No shrinkage figure, no crazing threshold, no haze value exists at program level — every one of them is configured per project and confirmed on parts.
How: The Three Axes, and the Hooks That Hold Them
3.1 What the record side actually holds
The material system registers both candidates, and reading the records precisely is half the battle. AS (SAN) is a registered grade, with the register noting that AS-type usage is decreasing per customer-driven requirements — a trend direction in the record, not a chemistry verdict on the resin. PETG is registered as a standard grade in its own right. Both also exist as recycled-content variants (PCR AS and PCR PETG), matching the discipline that runs across the material system: the recycled-content percentage is recorded per project, where project or specification evidence supports it, and no fixed figure is published.
The product side adds family-level texture. The cream jar family records 25 catalog models with PP+PETG jar-and-cap constructions — the working example of PETG in a heavy-wall transparent program. The airless family's material records include AS-type combinations (an AS/PCTG row) alongside PETG, and the lipstick family records catalog shell materials across ABS, PET, PETG, AS, and PMMA. None of these rows is a recommendation; each is a record that a given material has been configured in that family for real projects. The buyer's question — "which resin for my part" — is answered at the intersection of these records and the project's own formula.
3.2 Chemical crazing: the compatibility conversation, per project
Crazing is the failure mode at the center of transparent resin selection: a molded part holding internal stress (molding stress, design stress, assembly stress) meets a chemical substance the material tolerates poorly under that stress, and the surface develops fine, crack-like micro-fractures — showing up as frost, silvering, or a loss of gloss on the wall. It is a material-chemistry mechanism, described here as engineering guidance: no threshold, no chemical resistance grade, and no stress value exists in the program records.
What the program does hold is the hook: the compatibility test, from the quality program, is the gate that pairs the molded part with the actual formula before release. A standard pattern is to expose the project's formula (or its representative phase) against the molded part under the project's contact conditions — fill, storage, and use as the project defines them — and to inspect the wall for the visual signatures of crazing under agreed lighting. The contact duration, the temperature, and the acceptance criteria are configured per project; the compatibility test's existence and scope are the program-level facts.
The direction of the conversation matters too. A project that plans a solvent-heavy formula behind a transparent jar wall should expect the compatibility conversation to come early, not as a release-day surprise. We do not rank AS against PETG here — ranking without project evidence would exceed the records — but the pattern is stable: the formula decides which resin gets the closer look, and the compatibility test delivers the verdict per project.
3.3 Transparency: acceptance is visual, per project
Transparency reads differently on a data sheet than in the hand. A molded heavy-wall part's optical behavior is shaped by the resin's base properties and by everything the part inherits: wall thickness gradients, mold surface finish, gate and flow patterns, and the thermal history of the processing run. Two parts from the same resin can differ in perceived clarity run to run; two resins can meet the same optical intent at very different wall thicknesses.
That is why the acceptance gate is visual and per project. The practice is to agree a physical reference with the customer — the highest-clarity accepted sample — and to approve parts against that reference under an agreed lighting setup, because no numeric transparency value is recorded at program level. Where a project wants a measurement, the measurement is configured per project against the reference, not against a published material metric.
Two practical notes follow. First, wall thickness is the lever: a transparent heavy-wall jar trades clarity against the robust feel that made the wall heavy in the first place — the trade is resolved per project by the customer's priority. Second, decorations compound the optical conversation: a decorated wall is accepted against the decorated reference, not the raw resin, because the decoration itself changes the visual. Both notes are process guidance; the records supply the registered grades and the family constructions, and the project supplies the acceptance sample.
3.4 Mold shrinkage: dimensions are machined, then confirmed
Shrinkage is the dimensional partner of transparency in a heavy-wall part. Every resin contracts as it cools in the mold, different resins contract differently, and the wall thickness profile of a heavy-wall part makes the internal stress distribution part of the dimensional outcome — thicker sections cool slower, so their contraction history differs from thin sections. The consequence for the part is guidance, not a number: the mold must be machined for the actual resin of the project, and the part's dimensions must be confirmed against the project specification.
The engineering position is straightforward. Mold and tooling development — including how a cavity is sized for a chosen resin — is a recorded capability of our manufacturing system, alongside injection molding and blow molding. The machining offsets, cooling parameters, and cycle values are configured per project, exactly like every other machinery-level parameter; no universal shrinkage number belongs in any record or any article. What is published is the capability: the mold development and the molding itself happen inside our manufacturing system, and the confirmation happens through dimensional checks against the project specification.
For heavy-wall parts specifically, the confirmation is worth scheduling around the cooling history: dimensions are most informative once the part has rested past the immediate post-mold state, and dimensional confirmation is repeated when the resin lot changes. These are scheduling preferences, not universal values, and they keep the heavy-wall dimensional story honest: the mold is machined for the project, and the part proves the result.
3.5 The decision order in practice
A practical sequence for a transparent heavy-wall project, drawn from everything above: (1) put the formula in front of the material early — the compatibility conversation filters the candidates before any tooling is touched; (2) agree the optical reference on real molded samples, because a data-sheet transparency figure does not survive contact with a thick wall; (3) lock the dimensional plan with the mold as the resin is confirmed; (4) run the compatibility check, the visual acceptance, and the dimensional confirmation as the release gates, all per project.
The records support every step without fabricating any chemistry. The registered grades answer "what can be configured"; the family records answer "where this has been configured before" — the cream jar family on PP+PETG, the airless family's AS/PCTG rows and PETG rows, the lipstick family across ABS/PET/PETG/AS/PMMA; the manufacturing records answer "who machines the mold and runs the shot". The numbers that remain — shrinkage, thresholds, haze — are the project's numbers, configured per project, and confirmed on parts before release.
<pre class="language-mermaid"><code>flowchart LR
A[Transparent resin<br/>AS vs PETG] –> B[Record anchors<br/>materials + family use]
B –> C[Chemical compatibility<br/>per project]
C –> D[Transparency acceptance<br/>visual per project]
D –> E[Molding control<br/>our manufacturing system]
E –> F[Part released per project]
</code></pre>
What: Verified Program Data and the Verification Hooks
- Material records: AS (SAN) is registered; the register notes AS-type usage is decreasing per customer-driven requirements (a trend direction, with no figures attached). PETG is registered as a standard grade;
- Recycled-content variants: PCR AS and PCR PETG are registered variants; the recycled-content percentage is recorded per project, where evidence supports it — there is no default figure;
- Cream jar family: 25 catalog models, with jar-and-cap constructions recorded in PP+PETG;
- Airless family: material records include AS-type combination rows (AS/PCTG) alongside PETG;
- Lipstick family: catalog shell materials recorded across ABS, PET, PETG, AS, and PMMA;
- Manufacturing capability: injection molding, blow molding, and mold/tooling development are registered capabilities of our manufacturing system; machinery-level parameters are not published;
- Quality hook (capability-level): the compatibility test exists in the quality program; thresholds and acceptance criteria are set per project;
- What is not claimed: no shrinkage values, no crazing or chemical-resistance thresholds, no haze or transparency metrics, and no resin ranking without project evidence.
Gotchas
- Crazing has no number in any record. Do not quote stress-crack thresholds or chemical resistance grades; the compatibility test is the hook, and its criteria belong to the project.
- The AS trend is direction-only. Decreasing AS-type usage per customer-driven demand is a recorded trend, not an engineering verdict on AS — per-project selection stays open.
- Transparency is accepted per part. A transparency "value" does not exist at program level; the reference sample and the lighting setup are per-project agreements.
- Shrinkage is machined, not quoted. Universal shrinkage figures are out of scope; the mold is machined for the project's resin, and dimensions are confirmed against the project specification.
- PCR variants carry per-project percentages. PCR AS and PCR PETG exist as registered variants, but a recycled-content percentage appears only where project or specification evidence records it.
- Family records are records, not rankings. The airless family's AS/PCTG rows and the lipstick family's five-material shell list state what has been configured — not which resin wins for a new formula.
- The formula comes first. A heavy-wall transparent part with an aggressive formula is a compatibility project from day one; letting chemistry surprises surface at release is the one failure mode this sequence cannot absorb.
Related Resources
- Categories: Jars · Bottles · Lipsticks
- Related insight: PCR Resin Processing & Color Drift · Wide-Mouth Jar Materials · The 12-Test Lab Matrix
- Quality & Testing Capabilities — compatibility testing and per-project acceptance of transparent parts · Customization — per-project resin selection and construction configuration