I blew my nose and 3 pieces of hard rubbery feeling substance came out. is it nasal polyps, what is it? is this harmful? attached pic to account.

Inspissated mucus: The most likely rubbery substance that you could blow out of the nose is inspissated (dried) mucus. It is extremely rare and I have never seen a patient blow out a nasal polyp. The rest of your question can only be answered by looking at your nose. Any other symptoms? A blood clot is a conceivable other possibility.

Nasal substance: This most likely dried nasal secretions combined with mucosal sloughing or even blood. You have have even has a oropharynx food product that refluxed into your nose if you were coughing or laughing at that moment. Polyps are part of the nasal lining and do not normally comeout with nasal blowing and require surgical removal. It may also be an infection (bacterial or fungal) and may need PCP exam.

Thick mucous: It is unlikely that you could blow polyps out of your nose. They are often removed surgically. I was not able to access your photo, but it sounds like formed or thick mucous. Unlikely to be harmful. See your regular doctor or an ENT, otolaryngologist, for complete evaluation if this problem continues.