Water absorption is how much water a tile takes in, measured as a percentage of its dry weight. It shows how dense and closed the tile body is.
A tile counts as vitrified, or porcelain, when its water absorption is 0.5% or less. That is group BIa in ISO 13006 and EN 14411. In India, "vitrified" is the trade word for exactly this group.
The absorption groups
ISO 13006 and EN 14411 sort pressed tiles into groups by absorption. The letter B means dry-pressed, which covers almost all Morbi floor and wall tiles:
- BIa: 0.5% or less. Porcelain or vitrified tiles.
- BIb: above 0.5% up to 3%. Dense stoneware.
- BIIa: above 3% up to 6%.
- BIIb: above 6% up to 10%.
- BIII: above 10%. Typical ceramic wall tiles.
For group BIa, the standard sets 0.5% as the limit for the average of the tested tiles, with no single tile above 0.6%. The US uses the same 0.5% line for porcelain under ANSI A137.1, tested to ASTM C373.
Our guide to ceramic, porcelain and vitrified tiles explains the product names behind these groups.
Why absorption matters
- Strength: a dense, low-absorption body is usually stronger and resists breaking better.
- Frost: water that gets into a tile can freeze, expand and crack it. Low absorption is the first condition for frost resistance, tested to ISO 10545-12.
- Stains: an open body can take in liquids. This matters most for unglazed and polished tiles.
- Duties: the HS code for tiles depends on absorption. Heading 6907.21 covers tiles of 0.5% or less, so the test result affects how your goods are classified.
How it is tested
ISO 10545-3 sets the method. Tiles are dried and weighed, then soaked in water by boiling or under vacuum, and weighed again. The weight gain, as a percentage of the dry weight, is the absorption.
The test needs whole tiles or cut pieces from several tiles, so it is a lab test. You cannot judge absorption reliably by dripping water on the face of a glazed tile, because the glaze hides the body.
What to ask the factory
Ask for a recent test report from an accredited lab, naming the product, size and thickness you are buying. Check the report gives the average and the individual results, and the test method. Our founding guide on reading a lab certificate shows what a sound report looks like.
For large or repeat orders, have a production lot tested, not just a sample sent months earlier. Body recipes and firing can change when a plant changes clay suppliers or fuel. A lot test confirms the tiles you are shipping are still BIa.
Next step
Water absorption is one of the simplest ways to confirm you are getting real vitrified tiles. We arrange lot testing at accredited labs before the balance is paid. To plan your order, book a free sourcing review.