Hi Amanda, It depends on the environment.For lowland tropical rainforest where the weather is really humid, we seal the underside. Or, if they are going to an outdoor covered patio where they get sun and rain then I seal the underside as well. Inside a living room they don't need a sealed underside but we do it upon request.
@@barbra429 They are not cushy rugs. the are floor coverings however you can put thin padding underneath. I like to use it for the kitchen rug where I spend a lot of time standing. Here is a blog about padding you can use.laurelsoriginals.com/non-slip-options-for-canvas-area-rugs/
for a free course on how to buy the right canvas and prepare it to make your own canvas flor cloth free checkout app.mastermind.com/account/masterminds/29055
the polyurethane I use is oil-based. that is what is available to me in Costa Rica. I know floorcloth makers who use Varathane water-based polyurethane in the US and Sherwin Williams SherCler Marine coating.