What the Sync Layer IsFive decisions per field. Defaults answer all five badly.
The Salesforce HubSpot data sync is the field-level layer beneath the integration: for every mapped field, which direction data moves, which system is authoritative, how records are matched to one another, which records are allowed to cross at all, and what happens when a write is rejected. Those five answers, multiplied across every field, are the sync.
Direction is set per object and then refined per field — two-way, always use Salesforce, or always use HubSpot. The sync rule only applies where the object-level setting is two-way; a one-way object setting overrides it. Ownership follows from direction: engagement and scoring data is authored in HubSpot, pipeline and account data in Salesforce, and genuinely shared fields are the small exception rather than the default.
Matching is where most duplicate problems originate. HubSpot deduplicates Salesforce leads and contacts by email address, and that is the only field used. Records that represent the same person under different addresses will not be recognised. Resolving them means surfacing create date and the Salesforce Contact and Lead IDs, then merging in the correct system first so the sync links the surviving pair instead of recreating the duplicate. HubSpot documents this behaviour in its duplicate-handling guidance.
Filtering is the inclusion list — an active HubSpot list that controls which contacts may sync into Salesforce. Contacts not on it stay in HubSpot. One exception matters and catches people out: records created first in Salesforce can still sync to HubSpot regardless of the list. Failure handling is the decision nobody makes: what should happen when a write is rejected. The default is nothing, which is how divergence compounds unseen.
Twopir Consulting specifies all five for every field and hands over the document. We are a Salesforce Partner and a HubSpot Partner working with growing and mid-market companies — and enterprise organisations — on complex CRM, integration and business system challenges. For the wider integration this layer sits inside, see how the Salesforce HubSpot integration works, or start at our Salesforce and HubSpot integration services.