Insert Materials (Tip-Ins, Gatefolds, Maps, Photo Sections)
Insert materials are any interior components that use a different paper type, finish, weight, or construction than the main text pages surrounding them. They include photo and color plate sections, gatefolds and foldouts, tip-in plates, maps, cards, pockets, and any other element that introduces a different material into the interior of the book. In practical terms: inserts are different materials inside the same book—and if they expand, stiffen, or flex differently from the surrounding pages, they can create visible variation, pull on the binding, or cause problems with trim, fold, and closure.
Where You'll Encounter Inserts
Inserts appear in a wide range of book types:
- Cookbooks with separate photography sections on glossy coated stock
- Art and photography books with premium plate sections
- Biographies and memoirs with a central photo section
- Textbooks and reference books with color plate sections or pull-out charts
- Travel guides with fold-out maps
- Children's books with gatefold illustrations or sticker inserts
- Collector editions with fold-out posters or supplementary materials
Types of Inserts
Photo Section / Color Plate Section
A section of pages—typically 8, 16, or 32 pages—printed on a different paper than the main text, most often a coated gloss or silk stock. These sections are printed as a complete signature and bound in at a specific point in the text block. They are the most common type of insert in mainstream publishing and the source of most insert-related complaints.
Gatefold
A gatefold is a page or section where two panels fold inward to meet at the center, like double doors, revealing a wide image or layout when opened. Gatefolds are often used for wide photographic spreads, large diagrams, or premium cover effects. The paper must fold cleanly at scored lines, and the folded panel must fit within the trimmed page size without sticking out.
Foldout
A foldout is a single page that folds out in one direction—typically outward from the book—to reveal a larger image, map, or chart. Common in travel books, field guides, instruction manuals, and collector editions. The paper used must be light enough to fold easily but durable enough to survive repeated folding without cracking or tearing at the fold line.
Tip-In
A tip-in is a separate sheet (or small group of sheets) that is individually glued to the text block at one edge—most often at the spine gutter—rather than being part of a folded signature. Tip-ins are used for individual plates, artwork reproductions, maps, and supplementary inserts. Because they are bonded with a thin strip of adhesive, tip-in adhesion is more vulnerable than that of a sewn signature.
Pockets, Cards, and Special Inserts
Some books include glued-in pockets holding separate items (cards, maps, CDs, USBs) or bound-in items like rulers, bookmarks, or reference cards. These introduce additional materials with their own thickness, stiffness, and adhesion requirements.
In simple terms: every time a book uses more than one paper type or introduces a non-paper element, the finished book must manage the differences in how those materials sit, flex, expand, and bond. When those differences are not accounted for in specification and production, the result is visible in the finished book.
Why Inserts Create Challenges
Inserts differ from surrounding text paper in multiple ways that matter:
- Thickness and caliper: heavier insert stock creates a step change in the spine thickness at that point, which can affect how the text block sits in the case and how trimming handles the stack.
- Surface finish: coated insert stock responds to adhesives differently from uncoated text paper and may require different adhesive systems or preparation for binding.
- Ink coverage: photo sections often carry very high ink coverage on coated stock, which affects weight distribution, moisture response, and adhesion.
- Moisture behavior: coated and uncoated papers expand and contract at different rates with humidity change. An insert section that behaves differently from surrounding text paper causes section-level distortion in the text block.
- Fold performance: maps and foldouts use paper that must fold and refold many times. Paper that is too stiff, too heavy, or has the wrong grain direction at the fold will crack, split, or tear.
- Adhesive compatibility: the smooth surface of coated insert stock offers less mechanical adhesion surface than uncoated text paper.
What Readers Notice
- "The glossy section is curling or wavy."
- "The photo pages don't sit flat—they buckle when the book is closed."
- "The fold-out map is torn or cracked at the fold line."
- "One of the plates has come loose."
- "The book won't close flat where that section is."
- "The foldout sticks out past the edge of the pages."
- "The photo section feels completely different from the rest of the book."
How Insert Materials Contribute to Problems
Waviness, Curl, and Section-Level Distortion
Coated photo sections are particularly prone to curl because coated paper has a more uniform structure that responds less evenly to moisture change. When the photo section is glued into the text block and the assembly dries, differential moisture response between the coated insert and the uncoated text paper can cause the insert section to curl against the text block. In a perfect-bound book, this can be visible as a bump or wave near that section.
High ink coverage on glossy sections amplifies this effect: very heavy solid printing on coated stock changes the weight distribution of the sheet and can increase curl tendency—especially when ink curing or drying was not fully complete before binding.
Trim and Alignment Issues
When a text block containing mixed-caliper inserts is trimmed, the cutting blade passes through paper of varying thicknesses at different points in the stack. Thick sections can cause slight knife deflection, resulting in uneven trim. Insert sections that were not assembled perfectly square contribute to pages that appear off-center or to an uneven top or bottom trim. In perfect binding, an insert section that shifts slightly during gathering can become visible as misaligned pages at that section.
Binding Stress and Closure Problems
A thick coated insert section introduces a concentration of material at its location in the spine. In perfect binding, this can create a stress point where the adhesive must bridge a step change in thickness. If the adhesive layer is not thick enough or flexible enough at this point, the spine can be weaker at the insert boundary. In sewn binding, insert sections must be sewn through or sewn to, and the needle must penetrate coated stock whose surface offers more resistance than uncoated text paper.
When a book won't close flat at the insert section, it is typically because the coated stock is stiffer than the surrounding pages and holds a slight curl introduced during printing or binding. This is a design and specification issue—it can be reduced but not always eliminated when coated inserts are used in primarily uncoated text blocks.
Tip-In Adhesion Failures
Tip-ins rely on a narrow strip of adhesive along one edge. On coated stock, the smooth surface reduces adhesive penetration. If the adhesive strip is too narrow, applied unevenly, or not well matched to the coated surface, the tip-in can detach under normal page-turning forces. Heavy tip-ins (thick plates, laminated cards) have more mechanical force acting on the adhesive strip than lightweight sheets.
Fold Failures
Gatefold and foldout paper must survive repeated folding. Failures occur when:
- The paper is too heavy or stiff for the fold—it creases but does not fold cleanly, or cracks at the fold line on the first use.
- Grain direction is perpendicular to the fold, causing the paper to resist the fold and crack along the fiber lines rather than bending cleanly.
- The fold line was not scored, or was scored with insufficient depth, so the paper does not fold at the intended point.
- The paper has high ink coverage exactly at the fold line, and the ink film cracks when the paper bends.
Common Look-Alikes
Insert Section Curl vs. Overall Book Warp
Book warp affects the entire text block or case—the book is curved or twisted overall. Insert section curl is localized—the pages near and within the insert section are distorted, but the rest of the book is flat. Checking whether the problem is isolated to the insert location or distributed through the whole book quickly separates these two causes.
Tip-In Detachment vs. Loose Binding
A tip-in coming loose is a single sheet (or small group of sheets) detaching from a glued edge. Loose binding typically means signatures or pages throughout the book are not well bonded at the spine. A tip-in failure is localized and directional (the sheet pulls away from one edge); spine binding failure is longitudinal (pages pull away from the spine).
Trim Variation at Insert vs. Design Intent
Some books intentionally use a slightly different size for inserts—map foldouts that extend beyond the page edge when opened, or plates with a slightly different trim. Check whether the apparent size variation appears intentional (consistent with design, announced on the insert itself) or random (the insert appears shifted, with uneven margins).
What Is Considered Acceptable
Normal variation that is not a quality defect:
- A slight difference in feel and texture between coated insert sections and surrounding uncoated text pages—this is inherent to mixed-stock books.
- A very mild tendency for the book to open naturally at the insert section due to different paper stiffness.
- Minor color appearance difference between insert and text sections due to different paper surface reflectance.
Likely a quality problem:
- A photo or plate section that is visibly curled or buckled, preventing the book from closing flat.
- A foldout or map that tears or cracks at the fold line on first use.
- A tip-in that detaches with minimal handling from a new book.
- Insert section pages that appear significantly misaligned with the surrounding text block.
What a Buyer Can Do
Insert-related defects are often photogenic and clear to document:
- Photograph the affected insert section by placing the open book flat and shooting from the side to show any curl or buckle clearly.
- For tip-in failures, photograph both the detached sheet and the area it came from, showing the adhesive remnant if visible.
- For fold failures, photograph the fold line clearly to show cracking, tearing, or whitening at the fold.
- Note the location in the book (page numbers, section description) and whether only one or all copies of the title are affected.
- Do not attempt to re-glue loose tip-ins with general-purpose glues—these often cause wrinkling, staining, or permanent damage to coated surfaces. A proper bookbinding PVA applied with a thin strip and adequate pressing is required.
Related Pages
- Text Paper (Interior Stock)
- Coated vs. Uncoated Paper
- Perfect Binding Adhesives (EVA / PUR)
- Book Warp (Binding Defects)
- Loose Pages (Binding Defects)