Hi Robin – with the lightweight fabric, you may be able to use a slightly lower temperature, and to avoid bubbles I like to use the edge of my iron and slide it outward, rather than using the large flat part. Then it’s important to press on the fabric with a rag or something as it cools so it can’t lift before the weld sets. You may still have an occasional bubble or wrinkle, but it should be airtight. Cheers!