Some Experimental Boats made from Coroplast and other Corrugated Plastic sheets.
Several designers have played with Corrugated plastics and made some usable boats. Using this type of boatbuilding method results in ultra light boats that are easily folded and transported. Here are a few.
Ken Simpson has produced several simple reliable and easy to build designs. He has made his folding choroplast boat plans available free. For some of his wooden boats see my take apart and folding boats page.
Ehow Article on Kayak Making Since there are no dimensions or diagrams its a tad hard to follow though. There is a photo that is interesting.
These 2 coroplast signs show commonly available sizes. The top sign seen in cross section, is 8mm thick. It is surprisingly stiff. To bend this would require some heating to soften the board. A similar thickness is used by the Folding Boats with no Parts.
The lower sign is 4mm thick and much more flexible. It can easily be scored and bent with no heat. Any boat made with this would require stiffening to be safe. Ken Simpson uses this for his folding boat. He adds a plywood floor and thwarts as well as side rails to stiffen the boat.
Because corrugated plastic is essentially 2 waterproof sheets with air spaces in between, any boat built of choroplast will float quite well IF THE SPACES DONT FILL UP WITH WATER. Ken seals the edges with tape and this would keep water out.
A 4 mm sheet of corrugated plastic will enclose about 11 litres of air which will support 11 Kilos. This is not quite enough to support a person standing up or even sitting but it will support you if you are lying in the boat. Make sure you have your pdf on too. If your coroplast centre fill up with water then you don't get this flotation.
This information is for general knowledge. Using non tested materials can be dangerous. If you build a coroplast boat be careful and make sure you test and use your boat in safe waters with appropriate personal flotation devices and backup help.
Coroplast is a trade name for Corrugated plastic sheet made in many colours and thicknesses. Coroplast is a US company. In other parts of the world other trade names might be better known. Examples are Plaskolite, Corplast, Coroboard, Corruboard, Polyflute, Intepro, Correx, Twinplast, Impraboard, Alylux are other tradenames. If you are looking for a local supplier Googling these alternatives might be helpful.
I have not personally tested these boats. I can't say if they are safe. These are experiments by people who like to play and design things. Be careful already!