Formic Acid 85% vs 99%: Which Grade to Buy

Both grades are the same molecule, methanoic acid (HCOOH, CAS 64-18-6), classified under HS 291511. The 99% grade is close to pure acid; the 85% grade is acid diluted with water to a concentration that is easier to store, pump and ship. Which one to buy is a question of where the acid will be used and who does the dilution.

At a glance

	Formic acid 85%	Formic acid 99%
Assay	85% min HCOOH	99% min HCOOH
Appearance	Clear, colourless to pale yellow liquid with a pungent odour
Freezing point	about -12 °C	about +8 °C
Acid delivered per tonne	850 kg	990 kg
UN number / class	UN 1779, class 8 (corrosive)	UN 1779, class 8 (corrosive)
Packaging	25 or 35 kg HDPE jerrycans, 250 kg HDPE drums, 1,200 kg IBC; about 20 MT per 20' container
Shelf life	24 months sealed, below 30 °C, away from oxidisers and bases
Typical buyers	Silage, feed acidification, on-site dilution	Leather, textile dyeing, rubber coagulation, chemical synthesis

Freezing point is the practical difference

Pure formic acid freezes at about 8 °C, so 99% drums stored in an unheated warehouse in winter arrive solid and must be thawed before pumping. The 85% grade stays liquid to roughly -12 °C. For buyers in cold climates, or for any site that stores acid outdoors, this alone usually decides the grade.

Compare prices per kilogram of acid, not per tonne of product

A tonne of 85% contains 850 kg of acid; a tonne of 99% contains 990 kg. Divide each quotation by the acid content before comparing. When freight is a large share of landed cost, 99% often wins on delivered acid despite the higher unit price, because you are not paying to ship 150 kg of water per tonne. When the acid will be diluted at the point of use anyway, and freight is short, 85% is normally cheaper overall.

Which grade for which use

• Silage preservation and feed acidification. Applied at roughly 3-5 litres per tonne of forage, formic acid is diluted heavily in use. Most farms and feed mills buy 85%: it handles more safely, freezes less easily and the concentration difference disappears at the dosing rate. See Formic Acid 85%.
• Leather pickling and deliming. Tanneries run controlled baths and prefer the higher assay for predictable pH shifts and less water added to the float. Usually 99%. See Formic Acid 99%.
• Textile dyeing. pH control in wool and polyamide dyeing; either grade works, 99% is the common specification in dye houses that already stock concentrated acids.
• Rubber coagulation and chemical synthesis. Where the acid takes part in a reaction rather than adjusting pH, water content matters and 99% is specified.

Handling and documents

Both grades are dangerous goods (UN 1779, class 8). Shipments need a dangerous-goods declaration, UN-approved packaging and an MSDS; sea freight rates for class 8 are higher than for general cargo, which is another reason to compare on delivered acid. Store in HDPE or stainless steel, never in mild steel, and keep away from oxidising agents and bases. Ask for the certificate of analysis showing assay, chloride, sulphate and iron for each lot.

Request a quotation for Formic Acid 85% or Formic Acid 99%, or read how Incoterms change the landed cost of a dangerous-goods shipment.