Balloons fall under the category of children's toys and in Europe, there is a legal requirement that requires toys to be tested to regulation EN 71-2 FLAMMABILITY. Foil and latex balloons are not fire-resistant and when exposed to an open flame and will burn. It is important to note that helium is not flammable.
Regulation EN 71-2 looks at many different factors including the presence of flammable materials that are not permitted in children's toys, how long items burn for, and how quickly flames spread. Different types of items have acceptable different rates.
In the case of balloons, the test is not whether the balloons burn. The test is whether the product meets the flammability tests deemed acceptable by EN 71-2. We do not manufacture any of our balloons. However, we believe all of our manufacturers test their products to meet flammability and safety requirements of children's toys.
The sample report below is from Flexmetal showing what a PASS for flammability on metallized balloons looks like.
METALLIZED BALLOON TEST REPORT