Unfortunately, the answer to this question is not simple.  The intent of most glass fusers who ask this question is to find out if Bullseye glass is compatible with glass made by another manufacturer. But COE (“coefficient of expansion“) by itself cannot tell you if two glasses are compatible. In order to know that a Bullseye glass is compatible with glass from another manufacturer, you must conduct your own tests.
Matching COEs does not ensure compatibility between glasses, no matter what you read or hear anywhere else. There are many different factors besides COE that determine compatibility between glasses. COE is just a single factor.
Our fusible glasses are factory-tested for compatibility with each other. We do not test for compatibility with other manufacturers’ glasses. We do not test for COE or rate our glasses with COE numbers. We do not claim to produce glasses that are rated “COE 90.”
All compatible Bullseye glasses are tested compatible with other Bullseye compatible glass.
We strongly recommend reading TechNote 3: Compatibility of Glasses, which explains this complex and important matter in greater depth.