src/main/resources/assets/mekanism/recipes/plasticblock_15.json

{
  "result": {
    "item": "mekanism:plasticblock",
    "data": 15,
    "count": 4
  },
  "pattern": [
    "SSS",
    "S S",
    "SSS"
  ],
  "type": "minecraft:crafting_shaped",
  "key": {
    "S": {
      "item": "mekanism:polyethene",
      "data": 2
    }
  }
}