Floss is mostly made of nylon and comes in disposable plastic packaging. Being small and lightweight, floss thread is part of the plastic products that most easily enter the environment. Luckily some alternatives to plastic floss exist. The two main options are bio-based plastic suitable for vegans and silk floss. The former biodegrade in an industrial compost the latter biodegrades in your backyard compost.
Bambaw Silk Floss is a great replacement for nylon floss. It is mint flavored and 100% natural and compostable.
Dental floss is made of natural Ahimsa silk, which is one of the strongest natural fibers and is therefore perfect for gliding between teeth without breaking. The floss is coated with candelilla wax. There are 2 dental floss refill rolls in the package, one of which is enough for about 200 uses. If you want dental floss in a reusable metal dispenser, look here.