{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "balloons-and-diaphragms",
 "name": "Balloons, gloves, inner tubes and silicone sheet as diaphragms",
 "kind": "standard",
 "category": "Hardware",
 "group": "Found & household materials",
 "year": null,
 "question": "What is the best diaphragm material for a Stirling engine?",
 "tags": [
  "diaphragm",
  "balloon",
  "membrane",
  "seal",
  "silicone",
  "stirling",
  "long earth society",
  "found materials"
 ],
 "aliases": [
  "balloon diaphragm stirling",
  "diaphragm material",
  "silicone sheet thickness",
  "balloon thickness mm",
  "diaphragm stirling engine",
  "inner tube rubber thickness"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 0,
 "url": "https://xemstudio.com/objects/balloons-and-diaphragms/",
 "sheet_txt": "https://xemstudio.com/objects/balloons-and-diaphragms/sheet.txt",
 "sheet": {
  "basis": "Measured thicknesses of common latex and silicone sheet sources; stretch limits from material data",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Party balloon (latex, 12 in): 0.15–0.25 mm wall, stretches 600%; cut the neck off and use the flat 'equator' zone. Nitrile glove: 0.10 mm (palm), low stretch, best for low-pressure diaphragms under Ø40. Bicycle inner tube (butyl): 0.9–1.1 mm, stiff, fine for Ø80+ with 5 mm travel. Silicone sheet: 0.25 / 0.5 / 1.0 mm, survives 230 °C, the only one for a hot-side diaphragm.",
   "Sizing: a diaphragm's effective area is about the mean of the clamp bore and the centre disc; for the 12 oz can engine (Ø66 can, 10 mL syringe swept 2 mL) a Ø50 clamp bore with a Ø25 centre disc and 3 mm of travel gives about 4.4 cm² × 0.3 cm = 1.3 mL per direction. The clamp rings in the can-engine kit are Ø40, Ø50 and Ø60 bore.",
   "Clamp the sheet flat and slack (not pre-stretched) between two printed rings on six M3 screws; a smear of silicone grease on the lower ring seals it. Balloon rubber dies in sunlight in a few weeks; silicone lasts years."
  ],
  "table": {
   "columns": [
    "material",
    "thickness_mm",
    "max_temp_c",
    "stretch",
    "use"
   ],
   "rows": [
    [
     "12 in latex balloon",
     "0.15–0.25",
     60,
     "600%",
     "cold-side diaphragm, Ø30–60"
    ],
    [
     "nitrile glove",
     0.1,
     80,
     "300%",
     "small low-pressure diaphragm"
    ],
    [
     "bicycle inner tube (butyl)",
     "0.9–1.1",
     100,
     "200%",
     "large diaphragm, long travel"
    ],
    [
     "silicone sheet",
     "0.25 / 0.5 / 1.0",
     230,
     "400%",
     "hot-side or long-life diaphragm"
    ],
    [
     "PE film (freezer bag)",
     0.05,
     70,
     "low",
     "displacer-rod seal only"
    ]
   ]
  }
 },
 "sheet_text": "Balloons, gloves, inner tubes and silicone sheet as diaphragms — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/balloons-and-diaphragms/  (CC BY 4.0)\nBasis: Measured thicknesses of common latex and silicone sheet sources; stretch limits from material data\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Party balloon (latex, 12 in): 0.15–0.25 mm wall, stretches 600%; cut the neck off and use the flat 'equator' zone. Nitrile glove: 0.10 mm (palm), low stretch, best for low-pressure diaphragms under Ø40. Bicycle inner tube (butyl): 0.9–1.1 mm, stiff, fine for Ø80+ with 5 mm travel. Silicone sheet: 0.25 / 0.5 / 1.0 mm, survives 230 °C, the only one for a hot-side diaphragm.\n- Sizing: a diaphragm's effective area is about the mean of the clamp bore and the centre disc; for the 12 oz can engine (Ø66 can, 10 mL syringe swept 2 mL) a Ø50 clamp bore with a Ø25 centre disc and 3 mm of travel gives about 4.4 cm² × 0.3 cm = 1.3 mL per direction. The clamp rings in the can-engine kit are Ø40, Ø50 and Ø60 bore.\n- Clamp the sheet flat and slack (not pre-stretched) between two printed rings on six M3 screws; a smear of silicone grease on the lower ring seals it. Balloon rubber dies in sunlight in a few weeks; silicone lasts years.\n\nmaterial  thickness_mm  max_temp_c  stretch  use\n12 in latex balloon  0.15–0.25  60  600%  cold-side diaphragm, Ø30–60\nnitrile glove  0.1  80  300%  small low-pressure diaphragm\nbicycle inner tube (butyl)  0.9–1.1  100  200%  large diaphragm, long travel\nsilicone sheet  0.25 / 0.5 / 1.0  230  400%  hot-side or long-life diaphragm\nPE film (freezer bag)  0.05  70  low  displacer-rod seal only\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Diaphragm (mechanical device) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Diaphragm_(mechanical_device)\n- Wikipedia: Toy balloon — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Toy_balloon\n- Long Earth Society: Engine builds (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/\n\nXem Studio scan: not needed; this is a published standard. The sheet is the geometry.\nAPI: https://xemstudio.com/api/geometry?object=balloons-and-diaphragms\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Diaphragm (mechanical device)",
   "url": "https://en.wikipedia.org/wiki/Diaphragm_(mechanical_device)",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Toy balloon",
   "url": "https://en.wikipedia.org/wiki/Toy_balloon",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds (videos and write-ups)",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "can-engine-printed-kit",
  "plastic-syringes",
  "o-rings-metric",
  "beverage-cans"
 ],
 "faq": [
  {
   "q": "What can I use as a Stirling engine diaphragm?",
   "a": "A latex balloon for the classic cold-side can engine, silicone sheet (0.5 mm) for anything hot or long-lived, nitrile glove for tiny engines, inner tube for big slow ones."
  },
  {
   "q": "How thick is a balloon?",
   "a": "0.15–0.25 mm uninflated at the equator; it thins to under 0.1 mm inflated. Use it flat and slack."
  },
  {
   "q": "What size diaphragm for a soda can Stirling?",
   "a": "Ø50 mm clamp bore with a Ø25 centre disc moves about 1.3 mL over 3 mm of travel, matched to a 12 oz can displacer."
  }
 ],
 "files_license": null,
 "offers": [],
 "markdown": "https://xemstudio.com/objects/balloons-and-diaphragms/index.md"
}