Tetra Organic Baby Cot Mattress (Firm). Tetra Cot Mattresses are filled with Australian Tea Tree Paperbark Flakes that are naturally anti-bacterial, naturally anti-allergy, naturally breathable and cool in summer and warm in winter. Each organic Tetra Cot Mattress comes complete with a removable organic cotton cover. These may be removed and washed (cold water only). Tetra Cot Mattresses are tested to comply to the Australian Standard AS/NZS 8811.1.