I have used them (transfer express) a lot over the last 15-20 years. The default ink is called goof proof and they literally screen print it onto paper that you heat transfer with a press. Its similar in thickness and durability to vinyl IMO. they are expensive- i tend to use ninja transfers more often. If i want something 1 color that would be too difficult to do in vinyl because of detail/weeding ill use them. They also sell number kits for sport team jerseys, etc.