Polish designers Beton have created the S - Chair Transformer, a polyethylene foam cover that transforms solid chairs into comfy armchairs.
A thin, rectangular sheet of polyethylene foam is laser cut to create the surface pattern and interlocking mechanism that holds the two ends together without any further fixings.
Here's some words from the designers:
S - chair transformers
A thin rectangle of polyethylene foam is laser-cut in such a way, that you can create a tube out of it without using glue or anything like that. Inside the tube you can place any chair (the uglier, the better) and then you can sit on it. The chair is transformed into a comfortable, waterproof armchair... At ﬁrst the standing tube might be misleading, and it is the easiest way of creating something out of almost nothing.