When evaluating a vacuum stretcher, prioritize TPU (Thermoplastic Polyurethane) or high-grade PVC materials that are durable, easy to clean, and resistant to punctures. The internal filling should consist of high-density polystyrene beads that redistribute evenly to provide rigid support once the air is evacuated. Ensure the stretcher has a load capacity of at least 150kg to 250kg to accommodate various patient sizes. Additionally, verify that the product is X-ray, CT, and MRI compatible, allowing for medical imaging without removing the patient from the device.