It has nothing to do with the coaster, a glass with a cold drink will develop beads of condensation which will run to the bottom of the glass. This can create a hermetic seal around the bottom edge of the glass. The water has enough surface tension to prevent air from getting in, when the glass is lifted , a vacumn is created between the glass and the coaster. The outside air pressure is greater than the pressure in the space and the resulting force presses the coaster to the glass.

Yes. All the coasters are put into ovens and baked to make them heat proof, they are then sealed with a heat - resistant sealant.

All i can say is that they arent break proof which means if they are dropped onto a hard surface they could break but they are hard wearing.

If your not completely satisfied with your product, you can return the product at your own cost for a full refund minus the post and packaging. Items have to be returned within 30 days from date of purchase. Products bought at a market must be returned back to the stall holder at original market item was purchased.