br Tyvek is the material used in most postal services. These envelopes will keep its contents safe, secured, clean, and dry. These envelopes are almost indestructible and they are made to withstand the rigorous shipping conditions. Tyvek envelopes may look like paper; however, it is made from 100 high-density polyethylene. So what are you going to do if have a stash of Tyvek envelopes at home or at the office? Thankfully, these products are highly recyclable.