RESEARCH NOTES · SEPTEMBER 26, 2026
Fabric stretch data
The figures below are published elongation at maximum test force or at break. They show directional behavior, but they are not recommended installation stretch settings. The supplier’s shade-sail category establishes the ten available product families.
| Fabric | Warp | Weft | Test / source |
|---|---|---|---|
| Alnet Extrablock FR | 71% | 74% | At break, ASTM D4595 · Alnet table |
| Gale Commercial 95™ 340 | 103.67% | 63% | At maximum force, ASTM D5034 · Gale brochure |
| Gale Commercial 95™ 340 FR | 88.7% | 49% | At maximum force, ASTM D5034 · Gale brochure |
| Gale DualShade® 350 | 79% | 62% | At maximum force, ASTM D5034 · Gale brochure |
| Gale DualShade® 350 FR | 79% | 71% | At maximum force, ASTM D5034 · Gale brochure |
| Gale Heavy 430 | 88% | 128% | At maximum force, ASTM D5034 · Gale profile |
| Gale Heavy 430 FR | 56% | 106% | At maximum force, ASTM D5034 · Gale profile |
| Polyfab™ Polytex+® | 75% | 61% | At break, ASTM D5034 · Polyfab table |
| Polyfab™ Comtex+® | 87% | 96% | At break, ASTM D5034 · Polyfab table |
| Polyfab Architec 400 | 87% | 96% | At break, ASTM D5034 · Polyfab table |
Calculating stretch
For original length L and chosen stretch s%, extended length = L × (1 + s/100). For example, a 10 ft strip at 2% becomes 10.2 ft, while a 10 ft strip at 5% becomes 10.5 ft. The builder rotates these directions with the grain angle and holds attachment corners in place.
A maximum-force or break percentage cannot predict stretch under installation loads. Fabric-specific working values require load-versus-strain curves, biaxial material properties, target pretension, edge construction, and structural form finding. Gale notes that biaxial properties are available on request. Polyfab publishes biaxial charts, but they do not establish one universal installation percentage.
Installation percentage guidance
Among the ten fabrics, the only quantified installed-stretch example located was a Gale Commercial Heavy 430 design report. Its form finder used approximately 1.2% compensation in warp and weft at 1.2 kN/m prestress for that project. This is a documented case, not a general manufacturer recommendation. No comparable published installation percentage was verified for the other nine fabrics. The dropdown therefore labels the original 2% / 5% values as a project example and keeps them editable. Maximum-force and break percentages in the table above must not be substituted for working stretch.
Roll widths, seams & cable pockets
The Alnet and all Gale families in this catalog list a nominal 9 ft 10 in roll width. Polytex+®, Comtex+®, and Architec 400 list 12 ft 6 in. “Folded” on some product pages describes the shipped roll and does not halve the listed nominal width.
Following the requested fabrication assumption, each panel gives up 4 in at an edge joined to another panel, for an 8 in deduction per join. For n equal-width panels, estimated coverage across the fabric grain is n × roll width − (n − 1) × 8 in. The builder uses the sail’s across-grain span to estimate panel count and draws two stitch lines at each join. Panel cutting and seam placement remain concept approximations.
Each outside edge bows inward with a catenary profile and shows a cable pocket. The pocket width and its own cutting allowance are not specified, so the panel-count calculation does not deduct them. Cable selections are ¼ in, 9/32 in, and 5/16 in. The rendered pocket and cable are enlarged for visibility; the selected diameter is reference information rather than a structural sizing recommendation.
Model scope
The default layout is a 20 × 20 ft square with opposing corners A/C at 10 ft and B/D at 15 ft. Post quantity can be expanded from four to ten; horizontal and direct distances are calculated for every pair of entered XYZ post coordinates. Each post has a separate editable hardware and chain allowance, which moves its fabric corner inward before the sail mesh and panel estimate are calculated. The preview triangulates the ordered perimeter into a fabric mesh with anchored posts, visual sag, and directional deformation. Its initial 2% and 5% inputs are example assumptions from the project brief. The display is a concept model, not a fabrication pattern or structural analysis.