Not sure what the problem is, I have no knowledge of OpenGL. However, try using an vanilla render type (like TRANSLUCENT_SHEET_LIT i think is one) and call the parent method in the renderParticle (don't draw anything with the buffer). It'll help you isolate your problem I think (and hope). Also, using vanilla's is a good idea, unless you want something complex, BasicParticleType and an existing IParticleRenderType will do the job.