# Molded Pulp Packaging: The Four Types and the Missing Tolerance _The type system is most of the specification, the one published number disagrees with itself, and the geometry does the work the material gets credit for._ **The short answer** **Molded pulp comes specified by process type and wall thickness, and the type system carries most of the specification.** Four types run from thick-wall trays down to thin-wall parts that look like thermoformed plastic. **No published tolerance exists.** The trade association that defines the types sets none, and neither does a converter's own design guide, so dimensional limits come onto your drawing or not at all. Molded pulp arrives in a specification looking simpler than it is. One material, one process family, and a part that either fits the product or does not. Then the quote comes back and the questions start. How close to the drawing will it hold, how much does the wall vary, and what happens to it in a humid warehouse. Those answers are thinner than the material's popularity suggests. The type system is well published and the performance numbers mostly are not, which catches buyers arriving from thermoformed plastic hardest. This reference covers what the type system specifies, and why its one published number disagrees with itself. It also covers what does the cushioning work, what the tooling allows, and how fiber answers to moisture. - **4 types** - The classification that is the spec - **7°** - Draft angle called standard - **No tolerance** - Published by anyone - **16×** - Desiccant demand against foam ## What You Are Actually Specifying The trade association defines four types, and naming one carries most of the specification with it. Each type implies a wall thickness range, a tooling arrangement and a surface finish. | Type | Wall thickness | Molds | Typical use | | --- | --- | --- | --- | | 1 — thick wall | 3/16 to 3/8 in (5–10 mm) | Single mold | Vehicle parts, furniture, nursery pots | | 2 — transfer molded | 1/8 to 3/16 in (3–5 mm) | Forming plus transfer | Egg cartons, trays, electronics | | 3 — thermoformed | 3/32 to 5/32 in (2–4 mm) | Multiple heated molds | Parts resembling molded plastic | | 4 — processed | Follows its base type | Base type plus treatment | Printed, die-cut or coated parts | Type 1 uses a single mold, so one face comes out smooth and the other rough. That is fine under a transmission casing and visible on a retail shelf. The same tooling also turns out plant, floral and nursery containers. Type 2 adds a transfer mold and brings one side to a relatively smooth finish, which is why egg cartons and electronics trays both land here. Type 3 runs in multiple heated molds and dries in the mold rather than in an oven. The hot pressing leaves the wall somewhat denser, with smooth surfaces and minimal draft. Type 4 is not a fourth process. It describes a secondary treatment laid over a Type 2 or Type 3 part, covering hot or after pressing, printing, coloring, die-cutting, perforating, embossing, special molds and special slurry additives. Type 2 has also spread well past the egg carton. The association lists newer designs in electronics, hospital disposables, electrical appliances, office equipment, tableware and produce trays, all at the same wall range. So a drawing that names only a type has named a family rather than a part. Now the part that catches people. The association publishing that system states no dimensional tolerance, no density, no basis weight and no test standard to go with it. That absence has a practical edge. For board you can write a material callout and name a test that proves it. Here the type and the wall are the whole of what the published system gives you. ## The One Number Everyone Publishes, and It Disagrees Wall thickness is the figure every source carries, which makes it the natural anchor for a specification. It is also where two authoritative sources part company. The association puts thermoformed thin wall at [2 to 4 millimeters](https://www.imfa.org/molded-fiber-masterclass/). A converter's published design guide puts nominal wall at 0.6 to 1.2 millimeters, with 0.8 used for many projects. Those ranges do not overlap, and they sit roughly three times apart. Neither source is obviously wrong, and neither says which measurement it means. > Figure: The gap between the two published ranges is wider than the thinnest range itself. Which turns wall thickness into a drawing question rather than a lookup. Name the figure you need and the point where it gets measured, because inheriting a published range imports somebody else's definition. The converter guide is clear about the trade either way. Thinner walls raise the risk of holes, wrinkles and surface defects, while thicker walls buy durability and cost material, cycle time and money. ## Geometry Does the Cushioning, Not the Material Anyone specifying cushioning arrives with a habit from foam, where density is the lever that moves performance. Molded pulp does not reward that habit. A peer-reviewed study of a pulp cushion built from truncated pyramid units varied geometry, wall thickness, unit depth and humidity. It found performance affected more by the structural factors of the unit than by the material characteristics. That is a different design problem. The shape of the formed feature carries the protection, so two parts of identical material and wall can perform differently because their ribs and pyramids differ. The collapse itself happens in stages. The study describes elastic deformation, then a first buckling, then sub-buckling, then densification, with rigidity highest early and dropping sharply once plastic deformation starts. The direction of travel is clear even where magnitudes are not. Repeated impacts, higher static stress and higher drop heights all reduced cushioning performance, and the study puts no number on any of the three. So the habit to drop is reading a pulp part the way you read a foam one. With foam the packaging foam density figure moves the result, and cushion curves plot exactly that. A pulp part is closer to a molded structure that happens to be made of fiber. The ceiling does not move, though. Whatever carries the load, it still has to land under the product fragility limit the product itself sets. ## What the Tooling Will and Will Not Give You Molded pulp parts release straight out of the tool, and that one fact sets most of the design envelope. Draft angle comes first. A converter's guide calls 7 degrees the industry standard, with more than that improving release, tool performance and consistency, and less than that bringing wrinkling, rougher surfaces and lower efficiency. True undercuts are simply unavailable. A negative draft cannot be molded because the part has to come straight off the tooling, so retention features get built another way. Wash-trimmed openings are that other way. Cutouts in a vertical wall can hold a product in place without any molded undercut doing the work. Edges come in two grades. Wash trim comes straight off the machine at the lowest cost with a natural edge, while die-cutting is a secondary operation buying a cleaner, sharper line. One practical trap sits at the end of the line. Trays nest for shipping, tight nesting makes them hard to separate, and small de-nesting posts are what let a line pull them apart one at a time. The guide puts no dimensions on those posts. Features get named and left unmeasured, which is the pattern across this whole subject. ## It Is Paper, So It Answers to Moisture Every property above belongs to a fiber part, which means the surrounding air is part of the specification. The cushioning study expects strength and resilience to decline with humidity as well as with repeated loads. That is the same behavior the rest of the paper packaging family shows. Sealed packaging is where it turns into arithmetic. Military formulas assign dunnage a desiccant demand by material, and cellulosic material takes 8.0 units per pound against 0.5 for synthetic foam. That is a sixteenfold difference for the same weight of dunnage. Swap a foam insert for a pulp one inside a barrier bag and the desiccant calculation changes far more than the swap looks like it should. Which is the whole specification in one line. Name the type, put the wall thickness and its measuring point on the drawing, design the geometry rather than the material, and account for the water the fiber will carry. ## Common Questions ### What tolerance can molded pulp hold? No published figure exists. The trade association that defines the type system states no dimensional tolerance, and a converter's own design guide states none either. Treat the tolerance as something to agree in writing with the supplier and put on the drawing, not something to look up. ### Which molded fiber type fits the job? Start from wall thickness and finish. Type 1 runs 5 to 10 mm with one rough face, and Type 2 runs 3 to 5 mm with one smooth side. Type 3 runs 2 to 4 mm with smooth surfaces close to molded plastic, and Type 4 is a secondary treatment on a Type 2 or 3 part. ### Why do published wall thicknesses disagree? Because the sources are measuring differently and neither says so. The association puts thin wall at 2 to 4 mm while one converter publishes a nominal 0.6 to 1.2 mm, roughly three times apart with no overlap. Specify the figure and its measuring point rather than citing a range. ### Can molded pulp replace foam one for one? Not by matching a material figure. Published work finds pulp cushioning governed more by the geometry of the formed feature than by the material, so the part has to be designed rather than substituted. Sealed packaging also changes, since cellulosic dunnage carries far more desiccant demand than synthetic foam. **How to weigh this page.** The type system and its wall thickness ranges come from the trade association that publishes them. The draft angle, undercut, trim and nesting detail comes from one converter's published design guide and describes that converter's practice. The cushioning findings come from the reachable abstract of a peer-reviewed study of one cushion geometry, and the directions it reports carry no magnitudes, so none are quoted here. The desiccant coefficients are from military formulas covered elsewhere on this site. Where a dimension governs a purchase, get it onto the drawing with its measuring point. **Key takeaways** - Naming one of the four molded fiber types carries most of the specification, because each implies a wall thickness range, a tooling arrangement and a surface finish. - No dimensional tolerance is published by the trade association or by a converter's design guide, so the tolerance belongs on the drawing or nowhere. - Published wall thickness ranges disagree by roughly three times, and neither source states which measurement it describes. - Cushioning is governed more by the geometry of the formed feature than by the material, which breaks the density habit carried over from foam. - Parts release straight from the tool, so 7 degrees of draft is called standard and true undercuts are unavailable at any price.