diff --git a/js/common/model/Particle.ts b/js/common/model/Particle.ts
index 0c2779f8..323df750 100644
--- a/js/common/model/Particle.ts
+++ b/js/common/model/Particle.ts
@@ -44,6 +44,7 @@ export type ParticleStateObject = {
   vy: number;
 };
 
+//TODO https://github.com/phetsims/gas-properties/issues/231 implement TPoolable ?
 export default class Particle {
 
   // These are settable in the Diffusion screen